Reduced symbol rate handshake signaling in ADSL systems

ABSTRACT

In an asynchronous digital subscriber line (ADSL) system comprising a central office High Speed ADSL Terminating Unit (HSTU-C) in bi-directional discrete multitone (DMT) communication with a remote High Speed ADSL Terminating Unit (HSTU-R), a method for improving handshake detection is provided by the present invention. The method comprises transmitting handshake signaling from the HSTU-C to the HSTU-R via a first subset of carrier sets at a first symbol rate and transmitting handshake signaling from the HSTU-C to the HSTU-R via a second subset of carrier sets at a second symbol rate, the second symbol rate being less than the first symbol rate.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present invention claims benefit of U.S. ProvisionalApplication No. 60/398,124, filed Jul. 25, 2002, and U.S. ProvisionalApplication No. 60/399,135, filed Jul. 30, 2002, the entireties of whichare incorporated by reference herein.

FIELD OF THE PRESENT INVENTION

[0002] The present invention relates generally to asynchronous digitalsubscriber line (ADSL) systems, and in particular, to systems andmethods for improving transmission performance in such systems.

BACKGROUND OF THE PRESENT INVENTION

[0003] With the increasing popularity of the Internet and othercontent-heavy electronic communication systems, there has been asubstantial need for reliable and affordable high bandwidth mediums forfacilitating data transmissions between service providers and theircustomers. In relation to the requirement that such mediums beaffordable to consumers, it was determined that the most cost-effectivemanner for providing service to customers was by using infrastructurealready present in most locations. Accordingly, over recent years, thetwo such mediums most widely meeting these requirements include thecable television (CATV) and the conventional copper wire telephonesystems such as a “plain old telephone service” (POTS) or an integratedservices digital network (ISDN).

[0004] Relating specifically to the adaptation of POTS telephone linesand IDSN lines to carry data at high-bandwidth or ‘broadband’ datarates, a number of Digital Subscriber Line (DSL) standards and protocolshave been proposed. DSL essentially operates by formatting signals usingvarious time domain equalization techniques to send packets over copperwire at high data rates. A substandard of conventional DSL is known asAsymmetric Digital Subscriber Line (ADSL) and is considered advantageousfor its ability to provide very high data rates in the downstream (i.e.,from service provider to the user) direction by sacrificing speed in theupstream direction. Consequently, end user costs are minimized byproviding higher speeds in the most commonly used direction. Further,ADSL provides a system that applies signals over a single twisted-wirepair that simultaneously supports conventional POTS or ISDN service aswell as high-speed duplex (simultaneous two-way) digital data services.

[0005] Two of the proposed standards for ADSL are set forth by theInternational Telecommunications Union, TelecommunicationStandardization Section (ITU-T). A first conventional ADSL standard isdescribed in ITU-T Recommendation G.992.1—“Asymmetric Digital SubscriberLine (ADSL) Transceivers”, the body of which is incorporated herein byreference. A second, more recently proposed standard is the G.992.2 or‘G.lite’ standard, further described in ITU-T RecommendationG.992.2—“Splitterless Asymmetric Digital Subscriber Line (ADSL)Transceivers”, also bodily incorporated by reference herein. The G.litestandard is a variant of the G.992.1 standard, with modificationsdirected primarily to work in a splitterless environment (i.e., withouta splitter at the remote user end to separate the voice traffic from thedigital data traffic).

[0006] Prior to any transmission of actual data between the centraloffice ADSL transceiver unit (ATU-C) and the remote ADSL transceiverunit (ATU-R), the two entities must first undergo a initializationprocedure designed to familiarize the two entities with each other,identify the bandwidth capabilities for the current session, and furtherfacilitate the establishment of a valid connection. Pursuant to ADSLstandards provided by the International TelecommunicationUnion—Telecommunication Standardization Sector (ITU-T), theseinitialization procedures comprise the following: 1) a handshakeprocedure; 2) a transceiver training session; 3) a channel analysissession; 4) an exchange session; and finally 5) an actual datatransmission session commonly referred to as “showtime.”

[0007] Specifics of the handshake procedure are set forth in ITU-TRecommendation G.994.1—“Handshake Procedures for Digital Subscriber Line(DSL) Transceivers”, the body of which is incorporated by referenceherein. The handshake procedure is designed to enable peer components toinitiate a communications session between each other and generallyincludes the exchange of several specific types of messages havingpredetermined formats. Examples of such messages include the following:capabilities list and capabilities list request messages; mode selectand mode request messages; various acknowledge and negative acknowledgemessages, etc. Each of the above messages is generally formulated by aprotocol processor responsible for ensuring compliance with therequirements for protocol communication.

[0008] Because the various ITU-T recommendations identified above aredesigned to provide guidance to ADSL developers in various geographiclocations, different circumstance may exists which impact the methodwith which the general recommendations are implemented. Accordingly,Annexes to the recommendations have been created that specificallyitemize the effect of particular scenarios upon the adoption of thegeneral recommendations. For example, due to noise and otherinterference generated by these ISDN systems, as well as the potentialadverse impact ADSL deployment may have on these existing systems,relatively severe performance limitations have been placed upon ADSLimplementation in these regions. Of particular interest in the presentapplication is the effect of a large network of conventional TCM-ISDN(Time Compression Multiplex ISDN) telephone lines on ADSL development.Annex C of the G.992.1 Recommendation directly relates to suchcircumstances.

[0009] As is understood in the art, the data stream of TCM-ISDN istransmitted in one or more TCM-ISDN Timing Reference (TTR) periods. Insuch systems, the CO transmits data streams in the first half of the TTRperiod and the CPE (customer premise equipment) transmits data streamsin the second half of the TTR period. Accordingly, for the correspondingADSL system, the ATU-C typically receives NEXT (near-end cross talk)noise from the ISDN in the first half of the TTR period and FEXT(far-end cross talk) noise from the ISDN in the second half of the TTRperiod. Conversely, ATU-R typically receives FEXT noise from the ISDN inthe first half of the TTR period and NEXT noise from the ISDN in thesecond half of the TTR period. In order to compensate for the effects ofthe NEXT and FEXT noise, the ATU-C often estimates the FEXT_(R) (FEXTnoise at receiver) and NEXT_(R) (NEXT noise at receiver) duration atATU-R, and the ATU-R estimates FEXT_(C) (FEXT noise at CO) and NEXT_(C)(NEXT noise at CO) duration at ATU-C, considering propagation delay ofthe subscriber line. Thereafter, the ATU-C transmits symbols bysynchronizing with the TTR_(C) and the ATU-R transmits symbols bysynchronizing with the TTR_(R) which is generated based upon thereceived TTR_(C). FIG. 1 illustrates a conventional timing model forISDN/ADSL systems.

[0010] Due the differing effects of NEXT and FEXT on ADSL transmissions,Annex C of the G.992.1 Recommendation suggests implementing a DualBitmapped (DBM) process for framing data prior to transmission using adiscrete multitone (DMT) transmission process. In this manner, symbolsare created differently depending upon whether they are transmittedduring a NEXT period or a FEXT period, with the ATU-C transmittingFEXT_(R) symbols using a Bitmap-FR (in FEXT_(R) duration), andtransmitting NEXT_(R) symbols using Bitmap-N_(R) (in NEXTR duration)according to the result of initialization. Similarly, the ATU-Rtransmits FEXT_(C) symbols using Bitmap-F_(C) (in FEXT_(C) duration),and transmits NEXT_(C) symbols using Bitmap-N_(C) (in NEXT_(C) duration)in the same manner. In accordance with Annex C, the FEXT_(R/C)transmission includes 128 symbols, while the NEXT_(R/C) transmissionincludes 217 symbols, resulting in a combined hyperframe of 345 DMTsymbols.

[0011] As a means of controlling symbol transmission, Annex C alsoaffords the ATU-C the capability to disable Bitmap-N_(C) andBitmap-N_(R), thereby disabling the transmission of anything but a pilottone during the NEXT TTR periods. This mode of transmission isconventionally referred to as FBM (FEXT Bitmapped) transmission. The FBMmode uses the DBM technique to transmit data only during FEXT intervals.Accordingly, the ATU-C transmits only the pilot tone during the NEXT_(R)symbol. Consequently, the ATU-R disables Bitmap-N_(C) and does nottransmit any signal during the NEXT_(C) symbol. The ATU-C selects theDBM or FBM mode during G.994.1 handshaking using a “DBM” bit.

[0012] Another scenario of interest in the present application is thatdiscussed in Annex A to the G.992.1 Recommendation, requirements forADSL systems operating in a frequency band above the POTS frequencyband. As is understood, in order to avoid interference with existingPOTS systems, shifts in the ADSL signal Power Spectral Density (PSD)must be made in particular frequency ranges.

[0013] Although the recommendations present in the various specificationidentified above have been implemented to avoid conflict andinterference with existing systems, there remains a need in the art ofADSL systems for methods and systems for improving both performance andrange of such systems without adversely effecting existing systems,thereby improving upon the recommendations described forth above.

[0014] Additionally, there is a need in the art of ADSL systems, forimproved systems that maintain compatibility with existing ADSL systemsand equipment and which may be implemented with minimal changes to bothequipment specification and technical recommendations.

SUMMARY OF THE PRESENT INVENTION

[0015] The present invention overcomes the problems noted above, andrealizes additional advantages, by providing for methods and systems forimproving ADSL performance and reach within the context of Annex Cand/or Annex A of the existing G.992.1 Recommendation, without requiringthe addition of a new Annex or significant complications to existingequipment or recommendations. These modes of operation are heretoforegeneralized as C.X modes of operation. The methods and systems disclosedherein may further be beneficially implemented to improve theperformance and reach in other contexts by those skilled in the artusing the guidelines provided herein.

[0016] In a first embodiment, an overlap frequency spectrum isimplemented with transmissions made in accordance with Annex C to theG.992.1 Recommendation. In particular, systems implementing both overlapand non-overlap modes are fully supported by the existing G.992.1Recommendation. Further, the partial overlap spectra of Annex C (FBMsOL,DBMsOL) for providing reduced NEXT interference are defined as a subsetof the full-overlap spectrum defined in Annex A of G.992.1. Accordingly,there is no need to define new annexes for operation in overlapped modesfor DBM as well as for FBM as it is well supported by the current AnnexC definition. In addition, the use of the existing code points forimplementing the proposed overlap modes does not violate the operationof the current systems and also enables interoperability with thecurrent frequency division multiplexing (FDM) systems thereby ensuringbackward compatibility with current FDM systems.

[0017] In accordance with one embodiment of the present invention, apower spectral density (PSD) mask for spectral shaping of a dual bit map(DBM) mode downstream transmission is provided. The PSD mask isrepresented by the equation: $\begin{matrix}{{PSD}_{DBMsOL} = {K_{ADSL\_ OL} \times \frac{C}{f_{0}} \times \frac{\left\lbrack {\sin \left( {\pi \frac{f}{f_{0}}} \right)} \right\rbrack^{2}}{\left( {\pi \frac{f}{f_{0}}} \right)^{2}} \times}} \\{{~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~}{{\frac{1}{1 + \left( \frac{f}{f_{LP3dB}} \right)^{12}} \times \frac{1}{1 + \left( \frac{f_{HP3dB}}{f} \right)^{6}}},{0 \prec f \prec \infty}}}\end{matrix}$

[0018] where PSD_(DBMsOL) represents the PSD mask, K_(ADSL) _(—) _(OL)represents a constant value, C represents a constant value, f representsa frequency of the downstream transmission, f₀ represents a constantvalue, f_(LP3dB) represents a 3 decibel (dB) low pass frequency andf_(HP3dB) represents a 3 dB high pass frequency. K_(ADSL) _(—) _(OL)preferably has a value between 0.0900 watts and 0.1200 watts and morepreferably has a value of 0.1104 watts. The constant f₀ preferably has avalue between 2.100 megahertz and 2.300 megahertz and more preferablyhas a value of 2.208 megahertz. The constant f_(LP3dB) has a valuesubstantially equal to $\frac{f_{0}}{2}.$

[0019] The constant f_(HP3dB) has preferably has a value between 100kilohertz and 150 kilohertz and more preferably has a value of 130kilohertz. The constant C preferably has a value between 0.1 and 10 andmore preferably has a value of 2.

[0020] In accordance with another embodiment of the present invention, apower spectral density (PSD) mask for spectral shaping of a far endcross talk (FEXT) bit map (FBM) mode downstream transmission isprovided. The PSD mask is represented by the equation: $\begin{matrix}{{PSD}_{FBMsOL} = {K_{ADSL\_ OL} \times \frac{C}{f_{0}} \times \frac{\left\lbrack {\sin \left( {\pi \frac{f}{f_{0}}} \right)} \right\rbrack^{2}}{\left( {\pi \frac{f}{f_{0}}} \right)^{2}} \times}} \\{{~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~}{{\frac{1}{1 + \left( \frac{f}{f_{LP3dB}} \right)^{12}} \times \frac{1}{1 + \left( \frac{f_{HP3dB}}{f} \right)^{8}}},{0 \prec f \prec \infty}}}\end{matrix}$

[0021] where PSD_(FBMsOL) represents the PSD mask, K_(ADSL) _(—) _(OL)represents a constant value, C represents a constant value, f representsa frequency of the downstream transmission, f₀ represents a constantvalue, f_(LP3dB) represents a 3 decibel (dB) low pass frequency andf_(HP3dB) represents a 3 dB high pass frequency. where PSD_(DBMsOL)represents the PSD mask, K_(ADSL) _(—) _(OL) represents a constantvalue, C represents a constant value, f represents a frequency of thedownstream transmission, f₀ represents a constant value, f_(LP3dB)represents a 3 decibel (dB) low pass frequency and f_(HP3dB) representsa 3 dB high pass frequency. K_(ADSL) _(—) _(OL) preferably has a valuebetween 0.0900 watts and 0.1200 watts and more preferably has a value of0.1104 watts. The constant f preferably has a value between 2.100megahertz and 2.300 megahertz and more preferably has a value of 2.208megahertz. The constant f_(LP3dB) has a value substantially equal to$\frac{f_{0}}{2}.$

[0022] The constant f_(HP3dB) has preferably has a value between 27kilohertz and 40 kilohertz and more preferably has a value of 32kilohertz. The constant C preferably has a value between 0.1 and 10 andmore preferably has a value of 2.

[0023] In an asynchronous digital subscriber line (ADSL) systemcomprising a central office ADSL Terminating Unit (ATU-C) inbi-directional overlap spectrum discrete multitone (DMT) communicationwith a remote ADSL Terminating Unit (ATU-R), a method is provided inaccordance with yet another embodiment of the present invention. Themethod comprises the step of transmitting a first handshake tone ateither a first DMT tone or a second DMT tone based at least in part on adistance between the ATU-C and ATU-R. In one embodiment, the firsthandshake tone is transmitted at the first DMT tone when the distancebetween the ATU-C and ATU-R is less than 6.2 kilometers and the firsthandshake tone is transmitted at the second DMT tone when the distancebetween the ATU-C and ATU-R is greater than or equal to 6.2 kilometers.In one embodiment, the first handshake tone is a Pilot tone, the firstDMT tone is tone 64 and the second DMT tone is tone 32. In anotherembodiment, the first handshake tone is a TCM-ISDN Timing Reference(TTR) tone, the first DMT tone is tone 48 and the second DMT tone istone 24. The ATU-C and the ATU-R preferably are in bidirectionalcommunication via a TCM-ISDN network.

[0024] The method further may comprise the step of transmitting a secondhandshake tone at either a third DMT tone or a fourth DMT tone based atleast in part on the distance between the ATU-C and ATU-R. The secondhandshake tone may be transmitted at the third DMT tone when thedistance between the ATU-C and ATU-R may be less than 6.2 kilometers andthe second handshake tone is transmitted at the fourth DMT tone when thedistance between the ATU-C and ATU-R is greater than or equal to 6.2kilometers. In one embodiment, the first handshake tone is a Pilot toneand the second handshake tone is a TCM-ISDN Timing Reference (TTR) tone,the first DMT tone is tone 64, the second DMT tone is tone 32, the thirdDMT tone is tone 48 and the fourth DMT tone is tone 24.

[0025] In accordance with yet another embodiment of the presentinvention, an asynchronous digital subscriber line (ADSL) system isprovided. The ADSL system comprises a central office ADSL TerminatingUnit (ATU-C) and a remote ADSL Terminating Unit (ATU-R) inbi-directional overlap spectrum discrete multitone (DMT) communicationwith the ATU-C. The ATU-C is adapted to transmit a first handshake toneat either a first DMT tone or a second DMT tone based at least in parton a distance between the ATU-C and ATU-R and the ATU-R is adapted toreceive the first handshake tone at either the first DMT tone or thesecond DMT tone. In one embodiment, the first handshake tone istransmitted at the first DMT tone when the distance between the ATU-Cand ATU-R is less than 6.2 kilometers and the first handshake tone istransmitted at the second DMT tone when the distance between the ATU-Cand ATU-R is greater than or equal to 6.2 kilometers. In one embodiment,the first handshake tone is a Pilot tone, the first DMT tone is tone 64and the second DMT tone is tone 32. In another embodiment, the firsthandshake tone is a TCM-ISDN Timing Reference (TTR) tone, the first DMTtone is tone 48 and the second DMT tone is tone 24. The ATU-C and theATU-R preferably are in bidirectional communication via a TCM-ISDNnetwork.

[0026] The ATU-C further may be adapted to transmit a second handshaketone at either a third DMT tone or a fourth DMT tone based at least inpart on the distance between the ATU-C and ATU-R. The second handshaketone may be transmitted at the third DMT tone when the distance betweenthe ATU-C and ATU-R may be less than 6.2 kilometers and the secondhandshake tone is transmitted at the fourth DMT tone when the distancebetween the ATU-C and ATU-R is greater than or equal to 6.2 kilometers.In one embodiment, the first handshake tone is a Pilot tone and thesecond handshake tone is a TCM-ISDN Timing Reference (TTR) tone, thefirst DMT tone is tone 64, the second DMT tone is tone 32, the third DMTtone is tone 48 and the fourth DMT tone is tone 24.

[0027] Further, the ATU-C may be adapted to transmit the first handshaketone at the first DMT tone when the distance between the ATU-C and ATU-Ris less than 6.2 kilometers and transmit the first handshake tone at thesecond DMT tone when the distance between the ATU-C and ATU-R is greaterthan or equal to 6.2 kilometers.

[0028] In an asynchronous digital subscriber line (ADSL) systemcomprising a central office High Speed ADSL Terminating Unit (HSTU-C) inbi-directional discrete multitone (DMT) communication with a remote HighSpeed ADSL Terminating Unit (HSTU-R), a method for improving handshakedetection is provided in accordance with an additional embodiment. Themethod comprises transmitting handshake signaling from the HSTU-C to theHSTU-R via a first subset of carrier sets at a first symbol rate andtransmitting handshake signaling from the HSTU-C to the HSTU-R via asecond subset of carrier sets at a second symbol rate, the second symbolrate being less than the first symbol rate. The first symbol ratepreferably is 539.0625 symbols per second and the second symbol ratepreferably is 269.53125 symbols per second. In one embodiment, thehandshake signaling is transmitted via the second subset of carrier setsat the second symbol rate after a handshake attempt between the HSTU-Cand the HSTU-R performed at the first symbol rate for both the first andsecond carrier sets has failed. The second subset of carrier setsincludes carrier sets with noise greater than noise present in the firstsubset of carrier sets, where the noise includes near end cross talk.The second subset of carrier sets preferably includes carrier set C43and the second subset of carrier sets preferably includes carrier setA43. The HSTU-C and HSTU-R preferably are in bidirectional communicationvia a TCM-ISDN network.

[0029] The method further may comprise the step of detecting, at theHSTU-R, a number of phase changes in a given time window of thehandshake signaling transmitted by the HSTU-C via the second subset ofcarrier sets to identify the second symbol rate. The method also maycomprise the step of receiving, at the HSTU-C, at least one handshakesymbol from the HSTU-R at the identified handshake symbol transmissionrate. The step of detecting the number of phase changes in a given timewindow of the handshake signaling includes separating the handshakesignaling transmitted by the HSTU-C into a first set of sub-symbols anda second set of sub-symbols for a given time window, the second set ofsub-symbols following the first set of sub-symbols, performing a fastfourier transform on each of the first set of sub-symbols, performing afast fourier transform on each of the second set of sub-symbols, summinga result of the fast fourier transforms performed on the first set ofsub-symbols, summing a result of the fast fourier transforms performedon the second set of sub-symbols, and multiplying the summed result fromthe first set of sub-symbols with the summed result of the second set ofsub-symbols to determine the number of phase changes in the handshakesignaling within the time window. The number of phase changes detectedwithin the time window may be proportional to the identified secondsymbol rate or the second symbol rate may be identified by the HSTU-Rwhen the number of phase changes is at or above a minimum number ofphase changes associated with second symbol rate.

[0030] In an asynchronous digital subscriber line (ADSL) systemcomprising a central office High Speed ADSL Terminating Unit (HSTU-C) inbi-directional discrete multitone (DMT) communication with a remote HighSpeed ADSL Terminating Unit (HSTU-R), a method for improving handshakedetection robustness is provided. The method comprises transmittinghandshake signaling via a first subset of carrier sets of a DMTtransmission bandwidth between the HSTU-C and HSTU-R at a first symbolrate, determining a presence of near end cross talk (NEXT) in a secondsubset of carrier sets of the DMT transmission bandwidth, andtransmitting the at least one handshake symbol via the second subset ofcarrier sets at a second symbol rate so that at least one sub-symbol ofthe at least one handshake symbol transmitted over the second subset ofcarrier sets is substantially unaffected by near end cross talk. Thefirst symbol rate preferably is 539.0625 symbols per second and thesecond symbol rate preferably is 269.53125 symbols per second. Thesecond subset of carrier sets preferably includes carrier sets C43and/or A43.

[0031] In accordance with an additional embodiment of the presentinvention, an asynchronous digital subscriber line (ADSL) system isprovided. The ADSL system comprises a central office High Speed ADSLTerminating Unit (HSTU-C) and a remote High Speed ADSL Terminating Unit(HSTU-R) in bi-directional discrete multitone (DMT) communication withthe HSTU-C. The HSTU-C is adapted to transmit handshake signaling to theHSTU-R via a first subset of carrier sets at a first symbol rate andtransmit handshake signaling to the HSTU-R via a second subset ofcarrier sets at a second symbol rate, the second rate being less thanthe first rate. The first symbol rate preferably is 539.0625 symbols persecond and the second symbol rate preferably is 269.53125 symbols persecond. The HSTU-C may be further adapted to transmit the handshakesignaling via the second subset of carrier sets at the second rate aftera handshake attempt between the HSTU-C and the HSTU-R performed at thefirst rate for both the first and second carrier sets has failed. Thesecond subset of carrier sets preferably includes carrier set C43 and/orA43.

[0032] In an asynchronous digital subscriber line (ADSL) systemcomprising a central office High Speed ADSL Terminating Unit (HSTU-C) inbi-directional discrete multitone (DMT) communication with a remote HighSpeed ADSL Terminating Unit (HSTU-R), a method for improving handshakedetection is provided in accordance with yet another embodiment of thepresent invention. The method comprises detecting, at the HSTU-R, anumber of phase changes in a given time window of a handshake signalingtransmitted by the HSTU-C to identify a symbol rate of the handshakesignaling. The method further may comprise transmitting anacknowledgement symbol from the HSTU-R to the HSTU-C at the identifiedsymbol rate. The method additionally may comprise receiving, at theHSTU-C, at least one handshake symbol at the HSTU-R at the identifiedsymbol rate.

[0033] The step of detecting the number of phase changes in a given timewindow of the handshake signaling transmitted by the HSTU-C to identifya symbol rate of the handshake signaling preferably includes separatingthe handshake signaling transmitted by the HSTU-C into a first set ofsub-symbols and a second set of sub-symbols for a given time window, thesecond set of sub-symbols following the first set of sub-symbols,performing a fast fourier transform on each of the first set ofsub-symbols, performing a fast fourier transform on each of the secondset of sub-symbols, summing a result of the fast fourier transformsperformed on the first set of sub-symbols, summing a result of the fastfourier transforms performed on the second set of sub-symbols, andmultiplying the summed result from the first set of sub-symbols with thesummed result of the second set of sub-symbols to determine the numberof phase changes of the handshake signaling within the time window. Thenumber of phase changes detected within the time window may beproportional to the identified symbol rate or the identified symbol ratemay be identified by the HSTU-R when the number of phase changes is ator above a minimum number of phase changes associated with theidentified symbol rate.

[0034] In accordance with one embodiment of the present invention, apower spectral density (PSD) mask for spectral shaping of anasynchronous digital subscriber line (ADSL) overlap spectrumtransmission over a plain old telephone system (POTS) is provided. ThePSD mask is represented at least in part by a plurality of break points,the plurality of break points including:

[0035] approximately −97.5 decibel-milliwatts per hertz (dBm/Hz) atapproximately 0 kilohertz (kHz);

[0036] approximately −97.5 dBm/Hz at approximately 4 kHz;

[0037] approximately −92.5 dBm/Hz at approximately 4 kHz;

[0038] approximately −36.5 dBm/Hz at approximately 25 kHz;

[0039] approximately −36.5 dBm/Hz at approximately 1104 kHz;

[0040] approximately −46.5 dBm/Hz at approximately 2208 kHz;

[0041] approximately −101.5 dBm/Hz at approximately 3925 kHz;

[0042] approximately −101.5 dBm/Hz at approximately 8500 kHz;

[0043] approximately −103.5 dBm/Hz at approximately 8500 kHz; and

[0044] approximately −103.5 dBm/Hz at approximately 11040 kHz.

[0045] In accordance with another embodiment of the present invention, apower spectral density (PSD) mask for spectral shaping of anasynchronous digital subscriber line (ADSL) non-overlap spectrum over aplain old telephone system (POTS) is provided. The PSD mask may berepresented at least in part by a plurality of break points, theplurality of break points including:

[0046] approximately −97.5 decibel-milliwatts per hertz (dBm/Hz) atapproximately 0 kilohertz (kHz);

[0047] approximately −97.5 dBm/Hz at approximately 4 kHz;

[0048] approximately −72.5 dBm/Hz at approximately 80 kHz;

[0049] approximately −36.5 dBm/Hz at approximately 138 kHz;

[0050] approximately −36.5 dBm/Hz at approximately 1104 kHz;

[0051] approximately −46.5 dBm/Hz at approximately 2208 kHz;

[0052] approximately −101.5 dBm/Hz at approximately 3925 kHz;

[0053] approximately −101.5 dBm/Hz at approximately 8500 kHz;

[0054] approximately −103.5 dBm/Hz at approximately 8500 kHz; and

[0055] approximately −103.5 dBm/Hz at approximately 11040 kHz.

[0056] In accordance with an additional embodiment of the presentinvention, a power spectral density (PSD) mask for spectral shaping ofan asynchronous digital subscriber line (ADSL) overlap spectrum over aplain old telephone system (POTS) is provided. The PSD mask may berepresented at least in part by a plurality of break points, theplurality of break points including:

[0057] approximately −97.5 decibel-milliwatts per hertz (dBm/Hz) atapproximately 0 kilohertz (kHz);

[0058] approximately −97.5 dBm/Hz at approximately 4 kHz;

[0059] approximately −92.5 dBm/Hz at approximately 4 kHz;

[0060] approximately −56.5 dBm/Hz at approximately 25 kHz;

[0061] approximately −56.5 dBm/Hz at approximately 1104 kHz;

[0062] approximately −46.5 dBm/Hz at approximately 2208 kHz;

[0063] approximately −101.5 dBm/Hz at approximately 3925 kHz;

[0064] approximately −101.5 dBm/Hz at approximately 8500 kHz;

[0065] approximately −103.5 dBm/Hz at approximately 8500 kHz; and

[0066] approximately −103.5 dBm/Hz at approximately 11040 kHz.

[0067] In accordance with another embodiment of the present invention, apower spectral density (PSD) mask for spectral shaping of anasynchronous digital subscriber line (ADSL) non-overlap spectrum over aplain old telephone system (POTS) is provided. The PSD mask may berepresented at least in part by a plurality of break points, theplurality of break points including:

[0068] approximately −97.5 decibel-milliwatts per hertz (dBm/Hz) atapproximately 0 kilohertz (kHz);

[0069] approximately −97.5 dBm/Hz at approximately 4 kHz;

[0070] approximately −92.5 dBm/Hz at approximately 80 kHz;

[0071] approximately −56.5 dBm/Hz at approximately 138 kHz;

[0072] approximately −56.5 dBm/Hz at approximately 104 kHz;

[0073] approximately −46.5 dBm/Hz at approximately 2208 kHz;

[0074] approximately −101.5 dBm/Hz at approximately 3925 kHz;

[0075] approximately −101.5 dBm/Hz at approximately 8500 kHz;

[0076] approximately −103.5 dBm/Hz at approximately 8500 kHz; and

[0077] approximately −103.5 dBm/Hz at approximately 11040 kHz.

[0078] In accordance with yet another embodiment of the presentinvention, a power spectral density (PSD) mask for spectral shaping ofan asynchronous digital subscriber line (ADSL) overlap spectrum over anintegrated digital services network (ISDN) is provided. The PSD mask maybe represented at least in part by a plurality of break points, theplurality of break points including:

[0079] approximately −90 decibel-milliwatts per hertz (dBm/Hz) atapproximately 0 kilohertz (kHz);

[0080] approximately −90 dBm/Hz at approximately 93.1 kHz;

[0081] approximately −62 dBm/Hz at approximately 209 kHz;

[0082] approximately −36.5 dBm/Hz at approximately 255 kHz;

[0083] approximately −36.5 dBm/Hz at approximately 1104 kHz;

[0084] approximately −46.5 dBm/Hz at approximately 2208 kHz;

[0085] approximately −101.5 dBm/Hz at approximately 3925 kHz;

[0086] approximately −101.5 dBm/Hz at approximately 8500 kHz;

[0087] approximately −103.5 dBm/Hz at approximately 8500 kHz; and

[0088] approximately −103.5 dBm/Hz at approximately 11040 kHz.

[0089] In accordance with another embodiment of the present invention, apower spectral density (PSD) mask for spectral shaping of anasynchronous digital subscriber line (ADSL) overlap spectrum over anintegrated digital services network (ISDN) is provided. The PSD mask maybe represented at least in part by a plurality of break points, theplurality of break points including:

[0090] approximately −90 decibel-milliwatts per hertz (dBm/Hz) atapproximately 0 kilohertz (kHz);

[0091] approximately −90 dBm/Hz at approximately 93.1 kHz;

[0092] approximately −62 dBm/Hz at approximately 209 kHz;

[0093] approximately −56.5 dBm/Hz at approximately 255 kHz;

[0094] approximately −56.5 dBm/Hz at approximately 1104 kHz;

[0095] approximately −46.5 dBm/Hz at approximately 2208 kHz;

[0096] approximately −101.5 dBm/Hz at approximately 3925 kHz;

[0097] approximately −101.5 dBm/Hz at approximately 8500 kHz;

[0098] approximately −103.5 dBm/Hz at approximately 8500 kHz; and

[0099] approximately −103.5 dBm/Hz at approximately 11040 kHz.

[0100] The terms “approximate” and “approximately,” as used herein,refer to a range that is preferably within +1%, more preferably within+3%, even more preferably within +5% and most preferably within +10% ofthe indicated value. For example, “approximately 100 kilohertz”preferably means 99-101 kilohertz, more preferably means 97-103kilohertz, even more preferably means 95-105 kilohertz, and mostpreferably means 90-110 kilohertz.

[0101] In accordance with one embodiment of the present invention, apower spectral density (PSD) mask for spectral shaping of anasynchronous digital subscriber line (ADSL) overlap spectrumtransmission over a plain old telephone system (POTS) is provided. ThePSD mask is represented at least in part by a plurality of break points,the plurality of break points including:

[0102] −97.5±5% decibel-milliwatts per hertz (dBm/Hz) at 0±5% kilohertz(kHz);

[0103] −97.5±5% dBm/Hz at 4±5% kHz;

[0104] −92.5±5% dBm/Hz at 4±5% kHz;

[0105] −36.5±5% dBm/Hz at 25±5% kHz;

[0106] −36.5±5% dBm/Hz at 1104±5% kHz;

[0107] −46.5±5% dBm/Hz at 2208±5% kHz;

[0108] −b 101.5±5% dBm/Hz at 3925±5% kHz;

[0109] −101.5±5% dBm/Hz at 8500±5% kHz;

[0110] −103.5±5% dBm/Hz at 8500±5% kHz; and

[0111] −103.5±5% dBm/Hz at 11040±5% kHz.

[0112] In accordance with another embodiment of the present invention, apower spectral density (PSD) mask for spectral shaping of anasynchronous digital subscriber line (ADSL) non-overlap spectrum over aplain old telephone system (POTS) is provided. The PSD mask may berepresented at least in part by a plurality of break points, theplurality of break points including:

[0113] —97.5±5% decibel-milliwatts per hertz (dBm/Hz) at 0±5% kilohertz(kHz);

[0114] −97.5±5% dBm/Hz at 4±5% kHz;

[0115] −72.5±5% dBm/Hz at 80±5% kHz;

[0116] −36.5±5% dBm/Hz at 138±5% kHz;

[0117] −36.5±5% dBm/Hz at 1104±5% kHz;

[0118] −46.5±5% dBm/Hz at 2208±5% kHz;

[0119] −101.5±5% dBm/Hz at 3925+5% kHz;

[0120] −101.5±5% dBm/Hz at 8500±5% kHz;

[0121] −103.5±5% dBm/Hz at 8500±5% kHz; and

[0122] −103.5±5% dBm/Hz at 11040±5% kHz.

[0123] In accordance with an additional embodiment of the presentinvention, a power spectral density (PSD) mask for spectral shaping ofan asynchronous digital subscriber line (ADSL) overlap spectrum over aplain old telephone system (POTS) is provided. The PSD mask may berepresented at least in part by a plurality of break points, theplurality of break points including:

[0124] −97.5±5% decibel-milliwatts per hertz (dBm/Hz) at 0±5% kilohertz(kHz);

[0125] −97.5±5% dBm/Hz at 4±5% kHz;

[0126] −92.5±5% dBm/Hz at 4±5% kHz;

[0127] −56.5±5% dBm/Hz at 25±5% kHz;

[0128] −56.5±5% dBm/Hz at 1104±5% kHz;

[0129] −46.5±5% dBm/Hz at 2208±5% kHz;

[0130] −101.5±5% dBm/Hz at 3925±5% kHz;

[0131] −101.5±5% dBm/Hz at 8500±5% kHz;

[0132] −103.5±5% dBm/Hz at 8500±5% kHz; and

[0133] −103.5±5% dBm/Hz at 11040±5% kHz.

[0134] In accordance with another embodiment of the present invention, apower spectral density (PSD) mask for spectral shaping of anasynchronous digital subscriber line (ADSL) non-overlap spectrum over aplain old telephone system (POTS) is provided. The PSD mask may berepresented at least in part by a plurality of break points, theplurality of break points including:

[0135] −97.5±5% decibel-milliwatts per hertz (dBm/Hz) at 0±5% kilohertz(kHz);

[0136] −97.5±5% dBm/Hz at 4±5% kHz;

[0137] −92.5±5% dBm/Hz at 80+5% kHz;

[0138] −56.5±5% dBm/Hz at 138+5% kHz;

[0139] −56.5±5% dBm/Hz at 1104+5% kHz;

[0140] −46.5±5% dBm/Hz at 2208±5% kHz;

[0141] −101.5±5% dBm/Hz at 3925±5% kHz;

[0142] −101.5±5% dBm/Hz at 8500+5% kHz;

[0143] −103.5±5% dBm/Hz at 8500±5% kHz; and

[0144] −103.5±5% dBm/Hz at 11040±5% kHz.

[0145] In accordance with yet another embodiment of the presentinvention, a power spectral density (PSD) mask for spectral shaping ofan asynchronous digital subscriber line (ADSL) overlap spectrum over anintegrated digital services network (ISDN) is provided. The PSD mask maybe represented at least in part by a plurality of break points, theplurality of break points including:

[0146] −90±5% decibel-milliwatts per hertz (dBm/Hz) at 0±5% kilohertz(kHz);

[0147] −90±5% dBm/Hz at 93.1±5% kHz;

[0148] −62±5% dBm/Hz at 209±5% kHz;

[0149] −36.5±5% dBm/Hz at 255±5% kHz;

[0150] −36.5±5% dBm/Hz at 1104±5% kHz;

[0151] −46.5±5% dBm/Hz at 2208±5% kHz;

[0152] −101.5±5% dBm/Hz at 3925±5% kHz;

[0153] −101.5±5% dBm/Hz at 8500±5% kHz;

[0154] −103.5±5% dBm/Hz at 8500±5% kHz; and

[0155] 103.5±5% dBm/Hz at 11040±5% kHz.

[0156] In accordance with another embodiment of the present invention, apower spectral density (PSD) mask for spectral shaping of anasynchronous digital subscriber line (ADSL) overlap spectrum over anintegrated digital services network (ISDN) is provided. The PSD mask maybe represented at least in part by a plurality of break points, theplurality of break points including:

[0157] −90±5% decibel-milliwatts per hertz (dBm/Hz) at 0±5% kilohertz(kHz);

[0158] −90±5% dBm/Hz at 93.1±5% kHz;

[0159] −62±5% dBm/Hz at 209±5% kHz;

[0160] −56.5±5% dBm/Hz at 255±5% kHz;

[0161] −56.5±5% dBm/Hz at 1104±5% kHz;

[0162] −46.5±5% dBm/Hz at 2208±5% kHz;

[0163] −101.5±5% dBm/Hz at 3925±5% kHz;

[0164] −101.5±5% dBm/Hz at 8500±5% kHz;

[0165] −103.5±5% dBm/Hz at 8500±5% kHz; and

[0166] −103.5±5% dBm/Hz at 11040±5% kHz.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0167] The present invention sets forth exemplary systems and methodsfor modifying the existing G.992.1, G.992.2, and G.994.1 Recommendationsas presented by the ITU-T for the purposes of increasing ADSL systemperformance and reach in geographic regions falling under therequirements of Annexes A and C to the G.992.1 Recommendation. Inaccordance with the present invention, such modifications relate to theimplementation of signals having overlapping and non-overlappingfrequency spectra, as well as manipulations of DBM and FBMimplementations. The exemplary systems and methods described herein maybe implemented in other contexts as appropriate without departing fromthe spirit or the scope of the present invention.

[0168] As an initial matter, it is heretofore submitted that theperformance enhancing modifications of the present invention are fullysupported by the current G.992.1/G.992.2 standard specifications,thereby resulting in uncomplicated and rapid implementation. Inparticular, as specified in G.992.1 § C.4.8. relating to Annex C,entitled “A TU-C Downstream transmit spectral mask”, the downstreamspectral (PSD) mask of Annex C may use the same masks as Annex A.Further, Annex A of G.992.1 specifies in § A.1.2 a PSD mask foroverlapped spectrum operation, as well as a PSD mask for reduced NEXTinterference into the ADSL upstream band in § A.1.3 (commonly referredto as FDM or non-overlap spectrum). As discussed above, FDM is thepredominant mode of operation in Annex C geographic regions, whether itis the DBM or FBM version.

[0169] Furthermore, § C.4.8 indicates that when C-MSG1 bit 16 of theinitialization sequence undertaken during the handshake process has avalue of 0, the PSD mask specified in § A.1.3 may be used. Conversely,when the C-MSG1 bit 16 is set to 1, the PSD mask specified in § A.1.2may be used. Annex A of G.992.1 states in § A.1.2.1 that the lower endof the pass-band spectrum is a manufacturer discretionary value and thathandshake initialization signals may be transmitted with allsub-carriers from index 1 to 255, with index 1 also being vendordiscretionary.

[0170] In addition to providing support for the adoption of overlappingspectra in Annex C regions, the current G.992.1/G.992.2 standardspecifications further enables a proper inter-working of overlap andnon-overlap implementations without any modifications to therecommendation. In § 10.1.2 of the main body of G.992.1, entitled“Transparency to methods of separating upstream and downstream signals”,it is stated that “Manufacturers may choose to implement thisRecommendation [G.992.1] using either frequency-division-multiplexing(FDM) or echo canceling (overlapped spectrum) to separate upstream anddownstream signals. The handshaking initialization procedure describedhere ensures compatibility between these different implementations byspecifying all upstream and downstream control signals to be in theappropriate, but narrower, frequency bands that would be used by anconventional FDD (frequency-division duplexing) transceiver, and bydefining a time period during which an overlapped spectrum transceivercan train its echo canceller.”

[0171] The above-reference section indicates that no negotiation isrequired between transmitter and receiver of different implementations(overlap vs. non-overlap) to interoperate. The downstream transmitter[CO operator] has the choice of transmitting a full spectrum, while thedownstream receiver can decide to process the whole or part of theusable spectrum. This aspect is further illustrated in section §7.11.1.1 (entitled “Data sub-carriers”): “The channel analysis signaldefined in § 10.6.6 allows for a maximum of 255 carriers (at frequenciesnΔf, n=1 to 255) to be used. The lower limit of n depends on both theduplexing and service options selected. For example, if an overlappedspectrum is used to separate downstream and upstream signals, then thelower limit on n is determined by the POTS splitting filters. However,if frequency division multiplexing (FDM) is used, the lower limit is setby the downstream-upstream separation filters. In all cases the cut-offfrequencies of these filters are completely at the discretion of themanufacturer, and the range of usable n is determined during the channelestimation [by the receiver]”. This last sentence indicates that the useof the overlap region is ultimately determined by the capability of thereceiver to process the lower part of the spectrum. An FDM receiverwould not take benefit of the lower spectrum. However, this inability ofthe receiver does not prevent its proper operation in any circumstanceor lower its performance. This aspect has been verified throughinteroperability lab testing with different vendor's implementations.

[0172] Finally, it has been determined that proper interoperabilitybetween overlapped and non-overlapped spectrum implementations does notrequire any special handling or exchange of messages in G.992.1.Information bit 16 assigned in C-MSG1 and R-MSG1 messages of the channelanalysis phase indicate the capability of the transmitter/receiver pairto process the lower part of the spectrum. It is also highlighted in thestandard that since the initialization sequence allows for inter-workingof overlapped and non-overlapped spectrum implementations, informationbit 16 assigned in C-MSG1 and R-MSG1 are for information only.

[0173] Referring now to FIG. 2, there is shown a block diagramillustrating a deployment guideline for ADSL systems implemented inaccordance with the present invention. In view of the above support withthen current G.992.1 and G.992.2 Recommendations, it has been determinedthat 99.9% of customer coverage may be provided with no modification tothe existing standards, but merely with a modification to the manner inwhich the standardized equipment is utilized. These customers typicallycomprise those within about 6.2 km of the CO. However, as FIG. 1 furtherindicates, additional loop lengths of between 6.2 and 7 km will also besupported with minor modification to existing standards.

[0174] Relating specifically to the handshake initialization procedurerequired to establish overlapped versus non-overlapped spectra, thesub-channel information fields “G.992.1 Annex C Spectrum frequencydownstream Npar(3) coding—Octet 1 thru. 4.” may be utilized to informthe CO and CPE of the possibility of using lower frequency bands. Thisspectrum information indicated in the Npar(3) fields associated withthis recommendation is currently of informative nature only. A summaryof indication bits and modes is presented in Table 1. TABLE 1ATU-C/ATU-R overlap capability DS Transmission spectrum G.994.1 SpectrumOverlap/Non-overlap frequency downstream Modes (C-MSG1/R-Msg1 bit 16)(Npar(3) octet 1 & 2) DBM FDM bit 16 = 0: No Overlap Bin > 32 FBM FDMbit 16 = 0: No Overlap Bin > 32 XOL bit 16 = 1: Overlap Bin > 6 XDD bit16 = 1: Overlap Bin > 6 FBM bit 16 = 1: Overlap Bin > 6

[0175] In accordance with the present invention, five different Annex Cmodes of operation may be supported as Annex C compliant modes. Inparticular, XOL, XDD, FBM-SOL, DBM-FDM, FBM-FDM are fully supported,with DBM-FDM and FBM-FDM being the convention Annex C modes as describedin Annex C of the G.992.1 Recommendation. As set forth in detail above,the first three modes are a subset of the general overlapped spectrumoperation defined in G.992.1 Annex A, while the latter two areconsidered as non-overlapped, or conventional Annex C, spectrumoperation. Further, while G.992.1 ensures proper inter-working ofoverlapped and non-overlapped spectrum implementations, it is left tothe downstream transmitter to use or not to use the overlapped spectrum,thereby resulting in easy backward compatibility with downstreamtransmitters without such capability.

[0176] With respect to the above the following points are to be noted:the CO operator typically has the sole control of the spectrummanagement, i.e. if the operator does not wish to operate in overlappedmode on its loops plant, the operator needs only to limit the ATU-Ctransmitter in the manner set forth in additional detail below.Accordingly, it is not necessarily required to negotiate the use ofoverlapped spectrum between transmitter and receiver, as it istransparent to the remote terminal. That is enabling the transmission ofthe overlapped spectrum generally will not affect adversely theperformance or the connectivity of a remote terminal. Therefore, inaccordance with one embodiment, the use of any overlapped modes XOL,XDD, FBM-SOL may remain under control of the CO.

[0177] The decision to operate in full-duplex XOL, or half-duplex XDD orFBM-SOL, in one embodiment, likewise preferably remains under control ofthe central office operator, as it is the case for the selection ofconventional FBM or DBM modes. Further, because of the diversity of theloop plants and noise environments, the five different Annex C modes ofoperation may be individually selectable at the direction of the centraloffice. The criteria to select one mode versus another preferably isleft to the discretion of the operator. An automatic or intelligentselection of the mode under control of the central office may beimplemented and the application is left to the operator's discretion andis within the scope of the present invention.

[0178] Relating specifically to the preferred XDD mode of operation,this mode of operation features utilization of overlapping spectrumhaving downstream full duplex (FEXT and NEXT) and upstream (FEXT only)transmission. As set for the above, selection of this mode istransparent to the downstream transceiver and results in easy andefficient implementation of the mode.

[0179] With the use of the overlap spectrum, Annex C describes threehalf-duplex modes: namely, FBM-FDM, FBM-SOL and XDD, with the latter twobeing supersets of the first one, while all three modes are a subset ofthe more generic DBMOL defined in G.992.1. It should be understood thatthe G.992.1 Recommendation allows alternate or continuous transmissiondownstream and alternate or continuous transmission upstream as a subsetof the DBMOL mode. The following describes the transparent bin selectionprocess that allows inter-working of overlap and non-overlapimplementations can be extended to allow proper operation betweenFBM-FDM, FBM-SOL and XDD.

[0180] As explained above, the inter-working of overlap and non-overlapimplementations of G.992.1 does not require prior negotiation betweentransmitter and receiver. While the ATU-C transmits an overlap or anon-overlap spectrum (at the operator's discretion) during the channelestimation phase, the receiver determines the range of usable binswithin the downstream transmit spectrum, depending on its capability tohandle the received signal in the lower part of the spectrum. The ATU-Rcommunicates to the ATU-C the actual bins used for downstream dataallocation. It is this transparent process by the receiver that ensuresinteroperability between FBM-FDM & FBM-SOL platforms on the one hand, orDBMOL, XOL and DBM-FDM platforms on the other hand without any modenegotiation.

[0181] Similar to the modes described above, the principle of“transparent bin-selection” at the receiver foroverlapping/non-overlapping spectra also may be applied to ensure thatthe half-duplex modes, namely FBM-FDM, FBM-SOL and XDD, interoperateseamlessly. Similar to the overlap mode selections the continuous (DBM)or alternate (FBM) pattern of the downstream transmission at “showtime”is determined first by the ATU-C transmit pattern during the handshakeinitialization and then by the ATU-R's ability to process a signalcontinuously or alternatively during the channel estimation phase.Specifically, the similarities with the overlap/non-overlapbin-selection process are: 1) during initialization, the selection oftransmitting in alternate fashion (FBM) or continuously (DBM) downstreamis under control of the ATU-C. It is similar to the choice of usingnon-overlap or overlap mode by the ATU-C; and 2) the C.X ATU-R receiverselects the bin location used for the transmission downstream inshow-time: if the C.X receiver senses signal in both NEXT and FEXTperiods during the channel estimation phase, it can allocate bins inboth periods and require transmission of data continuously. However, ifthe ATU-R receiver does not sense signal during the NEXT period, becausethe ATU-C does not transmit during this period, the ATU-R will allocatebins only during the FEXT period.

[0182] The overlap/non-overlap bin-selection process clarifies how XDDor FBM systems can interoperate. Connecting to a C.X ATU-C, an XDD ATU-Rcapable of processing data continuously may easily request transmissionof data downstream continuously, while an FBM ATU-R will not be affectedby the ATU-C 's transmission during the NEXT period duringinitialization and will request transmission downstream in FEXT periodsonly in showtime.

[0183] While the control of the ATU-C transmitter allows operation ofFBM and DBM downstream, control of the FBM and DBM upstream can beaccomplished via the DBM bit defined in G.994.1. This enablesindependent operation of the ATU-C and ATU-R. Therefore, to accomplishproper inter-working of C.X modes, it is submitted that: 1) the ATU-Ckeeps complete control of the downstream transmission characteristics:ATU-C decides to transmit downstream continuously or alternativelyduring initialization independent of the upstream transmission pattern;and 2) the ATU-C controls the upstream transmission pattern throughappropriate ATU-C through ATU-R signaling, independently of thedownstream transmission pattern.

[0184] To achieve this last goal, the ATU-C CL/MS message NPar(2) bitDBM of G.994.1 may be utilized. However, in order to decouple thepattern of the downstream and upstream transmission characteristics, therestriction in the current definition of the DBM bit that requires FBMoperation in downstream and in upstream simultaneously preferably islifted.

[0185] For the XDD mode, setting the NPar(2) bit DBM to 1 of G.994.1generally forces the CPE transmitter to transmit upstream during FEXTonly in the initialization and data mode phases. ATU-C will continuouslytransmit downstream during NEXT and FEXT periods using the overlapspectrum. A C.X ATU-R will be able to allocate bins in FEXT and NEXT andoperate continuously in the downstream path and alternately in theupstream path in XDD mode. An FBM only ATU-R will not allocate bins inNEXT and operate in true FBM mode. For the FBM mode, setting the NPar(2)bit DBM to 1 in accordance with G.994.1 typically adapts the CPEtransmitter to transmit upstream during FEXT only in the initializationand data mode phases, as it is done for FBM FDM. ATU-C will transmitdownstream during FEXT periods.

[0186] In Tables C-3 through C-6 of G.994.1 (Tables 2-5, respectively),the following changes are recommended in sections C.7.2.1, C.7.2.2,C.7.3.1 and C.7.3.2 (relating to of ATU-C CL/MS message NPar(2) DBM bitdefinitions in G.994.1):

[0187] C.7.2.1 CL Messages (Supplements § 10.2.1) TABLE 2 Modificationsto Table C-3 (ATU-C CL message NPar(2) bit definitions) NPar(2) bitDefinition DBM If set to ZERO, this bit may indicate Bitmap-N_(R) andBitmap-N_(C) are enabled (Dual Bitmap mode) and are used to transmitdata. If set to ONE, this bit may indicate Bitmap- N_(C) is disabled(FEXT Bitmap mode upstream), i.e. only Bitmap-F_(C) is used to transmitdata by ATU-R. Bitmap-N_(R) may be enabled (Dual Bitmap modedownstream). This mode selection may be only performed by the ATU-C. Ifit is set to ONE in a CL message, it must be set to ONE in subsequent MSmessages from, either the ATU-C or ATU-R (only applicable for G.992.1Annex C).

[0188] C.7.2.2MS Messages (Supplements § 10.2.2) TABLE 3 Modificationsto Table C-4 (ATU-C MS message NPar(2) bit definitions) NPar(2) bitDefinition DBM If set to ZERO, this bit may indicate Bitmap-N_(R) andBitmap-N_(C) are enabled (Dual Bitmap mode) and are used to transmitdata. If set to ONE, this bit may indicate Bitmap- N_(C) is disabled(FEXT Bitmap mode), i.e. only Bitmap-F_(C) is used to transmit dataATU-R. Bitmap-N_(R) may be enabled (Dual Bitmap mode downstream). Thismode selection may be only performed by ATU-C. This bit may be set toONE if it was set to ONE in a previous CL message (only applicable forG.992.1 Annex C).

[0189] C.7.3.1CLR Messages (Supplements § 10.3.1) TABLE 4 Modificationsto Table C-5 (ATU-R CLR message NPar(2) bit definitions) Npar(2) bitDefinition DBM This bit may be set to ONE.

[0190] C.7.3.2MS Messages (Supplements § 10.3.2) TABLE 5 Modificationsto Table C-6 (ATU-R MS message NPar(2) bit definitions) Npar(2) bitDefinition DBM If set to ZERO, this bit may indicate Bitmap-N_(R) andBitmap-N_(C) are enabled (Dual Bitmap mode) and are used to transmitdata. If set to ONE, this bit may indicate Bitmap-N_(C) is disabled(FEXT Bitmap mode upstream), i.e. only Bitmap-F_(C) is used to transmitdata by ATU-R. Bitmap-N_(R) may be enabled (Dual Bitmap modedownstream). This mode selection may be only performed by ATU-C. Thisbit may be set to ONE if it was set to ONE in a previous CL message(only applicable for G.992.1 Annex C).

[0191] Relating now to the addition of two reduced NEXT overlapped PSDmasks for inclusion in Annex C of G.922.1, there are defined anoverlapped mask with spectral shaping for use with FBM mode and anotheris defined for use with DBM mode. Overlapping of the downstream bandwith the upstream band allows for performance improvement of the Annex Cdownstream channel, while the spectral shaping controls the spectralcompatibility with other systems in the cable. The shaped overlap maskfor use with dual bit map mode of operation is commonly referred to asthe DBMsOL mask and the mask for use with FEXT bit map mode of operationis commonly called the FBMsOL mask. Both of these masks are spectrallycompatible with the First Group systems (namely Annex A, Annex C DBM,Annex C FBM, and TCM-ISDN) in accordance with the criteria set forth bythe Telecommunication Technology Committee (TTC) in Japan, within thedefinition of C.X modes of operation. It is therefore submitted that theDBMsOL and FBMsOL masks be incorporated in Annex C of G.992.1 andG.992.2 for enhanced performance and reduced NEXT applications.

[0192] The Dual Bit Map Overlap (DBMOL) PSD mask represents to thecurrent ADSL overlap mask that extends the usual downstream bandwidthdown to just above the POTS band (25.875 KHz) and is defined in G.992.1,Annex A, section A1.2. The same mask definition is provided in FIG. 3and Equation 1. Equation 1 provides an explicit form of the ITU ADSL_OLPSD template that matches the mask displayed in FIG. 3, used for DBMOLdownstream. Table 6 describes the break points of the PSD mask. Notethat unless otherwise indicated, the PSD mask associated with a spectrummanagement class, as defined by Equation 1 below, is equal to the PSDtemplate plus 3.5 decibels (dB). $\begin{matrix}\begin{matrix}\begin{matrix}{{PSD}_{{ADSL\_ OL},{{ds}\text{-}{Disturber}}} = {K_{{ADSL\_ OL},{ds}} \cdot \frac{2}{f_{0}} \cdot \frac{\left\lbrack {\sin \left( {\pi \frac{f}{f_{0}}} \right)} \right\rbrack^{2}}{\left( {\pi \frac{f}{f_{0}}} \right)^{2}} \cdot}} \\{{~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~}{{\frac{1}{1 + \left( \frac{f}{f_{LP3dB}} \right)^{12}} \cdot \frac{1}{1 + \left( \frac{f_{HP3dB}}{f} \right)^{8}}},{0 \prec f \prec \infty}}}\end{matrix} \\{f{\text{:}\quad\lbrack{Hz}\rbrack}} \\{{f_{0} = {2.208 \times {10^{6}\quad\lbrack{Hz}\rbrack}}},{f_{LP3dB} = {\frac{f_{0}}{2}\left( {G{.992}{.1}} \right)}},} \\{{f_{HP3dB} = {25.875 \times {10^{3}\quad\lbrack{Hz}\rbrack}}},{K_{{ADSL\_ OL},{ds}} = {0.1104\quad\lbrack W\rbrack}}}\end{matrix} & {{EQ}.\quad 1}\end{matrix}$

TABLE 6 Explicit attenuation and levels of DBMOL downstream spectralMask Frequency f(KHz) PSD (dBm/Hz) Peak values 0 < f < 4 −97.5 dBm/Hzpeak    4 < f < 25.875 −92.5 + 21 log₂(f/4) 25.875 < f < 1104   −36.5dBm/Hz peak 1104 < f < 3093 −36.5 − 36 log₂(f/1104) 3093 < f       −90dBm/Hz

[0193] The PSD template associated with the DBM shaped overlap (DBMsOL)mode preferably is defined by Equation 2. The DBMsOL spectral mask leveltypically is lower than the full overlap mask of DBMOL and thus is ITU-TG.992.1 compliant. DBMsOL exhibits a much greater high pass cornerfrequency (˜130 KHz) than DBMOL (25.875 KHz) to ensure spectralcompatibility with First Group system upstream channels. It also uses a3^(rd) order high-pass filter rolloff as opposed to the 4^(th) orderrolloff of the full overlap mask of DBMOL. Based on extensivesimulations, this shaped overlap mask has been recognized to be fullyspectrally compatible with other systems in the Japan access network,within the C.X modes of operation. $\begin{matrix}\begin{matrix}\begin{matrix}{{PSD}_{{DBMsOL},{{ds}\text{-}{Disturber}}} = {K_{{ADSL\_ OL},{ds}} \cdot \frac{2}{f_{0}} \cdot \frac{\left\lbrack {\sin \left( {\pi \frac{f}{f_{0}}} \right)} \right\rbrack^{2}}{\left( {\pi \frac{f}{f_{0}}} \right)^{2}} \cdot}} \\{{~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~}{{\frac{1}{1 + \left( \frac{f}{f_{LP3dB}} \right)^{12}} \cdot \frac{1}{1 + \left( \frac{f_{HP3dB}}{f} \right)^{6}}},{0 \prec f \prec \infty}}}\end{matrix} \\{f{\text{:}\quad\lbrack{Hz}\rbrack}} \\{{f_{0} = {2.208 \times {10^{6}\quad\lbrack{Hz}\rbrack}}},{f_{LP3dB} = {\frac{f_{0}}{2}\left( {G{.992}{.1}} \right)}},} \\{{f_{HP3dB} = {130 \times {10^{3}\quad\lbrack{Hz}\rbrack}}},{K_{{ADSL\_ OL},{ds}} = {0.1104\quad\lbrack W\rbrack}}}\end{matrix} & {{EQ}.\quad 2}\end{matrix}$

[0194] The FBMsOL template preferably follows the generic shape of thePSD template defined by Equation 1. To ensure spectral compatibilitywith Annex C DBM upstream, FBMsOL moves the high pass corner frequencyfrom approximately 25.875 kHz up to approximately 32 kHz.

[0195] In accordance with another embodiment of the present invention, anew high speed dual bit map (HSDBM) system is provided based on ITU-TG.992.1 compliant Annex C dual bit map (DBM) mode, to address thegrowing need for high speed ADSL in Japan. HSDBM makes use of theoverlapped spectra defined in the ITU-T Recommendation G.992.1, and isdesigned to operate at speeds in excess of 12 megabits/s (Mb/s).Spectral compatibility simulations, using a TTC-compliant simulator,demonstrate that systems implementing the DBM full overlap mask can bedeployed up to 1.5 km and maintain spectral compatibility with the FirstGroup systems. Systems deployed using the DBM shaped overlap (DBMsOL)mask can be deployed up to 2.0 km and maintain spectral compatibilitywith First Group systems. The DBMsOL mask preferably is identical tothat used for XOL and XDD systems for C.X. The computed deploymentguidelines are such that the HSDBM systems are deployed in the samequadrant as First Group systems.

[0196] The DBMOL downstream spectral mask is equivalent to the ADSLoverlap mask (ADSL_OL) as defined in G.992.1, Annex A, section A1.2.ADSL_OL extends the downstream bandwidth to the POTS band (25.875 KHz).Equation 3 provides an explicit form of the ITU ADSL_OL PSD templatethat matches the mask displayed in FIG. 3 used for DBMOL downstream.$\begin{matrix}\begin{matrix}{{PSD}_{DBMsOL} = {K_{ADSL\_ OL} \times \frac{C}{f_{0}} \times \frac{\left\lbrack {\sin \left( {\pi \frac{f}{f_{0}}} \right)} \right\rbrack^{2}}{\left( {\pi \frac{f}{f_{0}}} \right)^{2}} \times}} \\{{~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~}{{\frac{1}{1 + \left( \frac{f}{f_{LP3dB}} \right)^{12}} \times \frac{1}{1 + \left( \frac{f_{HP3dB}}{f} \right)^{6}}},{0 \prec f \prec \infty}}}\end{matrix} & {{EQ}.\quad 3}\end{matrix}$

[0197] where PSD_(DBMsOL) represents the PSD mask, K_(ADSL) _(—) _(OL)represents a constant value, C represents a constant value, f representsa frequency of the downstream transmission, f₀ represents a constantvalue, f_(LP3dB) represents a 3 decibel (dB) low pass frequency andf_(HP3dB) represents a 3 dB high pass frequency. K_(ADSL) _(—) _(OL)preferably has a value between 0.0900 watts and 0.1200 watts and morepreferably has a value of 0.1104 watts. The constant f₀ preferably has avalue between 2.100 megahertz and 2.300 megahertz and more preferablyhas a value of 2.208 megahertz. The constant f_(LP3dB) has a valuesubstantially equal to $\frac{f_{0}}{2}.$

[0198] The constant f_(HP3dB) has preferably has a value between 100kilohertz and 150 kilohertz and more preferably has a value of 130kilohertz. The constant C preferably has a value between 0.1 and 10 andmore preferably has a value of 2.

[0199] The DBMsOL spectral mask preferably uses the same PSD masks asXOL and XDD systems defined by Equation 4 below. However, when comparedto the DBMOL mask, the DBMsOL mask uses a 3^(rd) order high-pass filter(as opposed to a 4^(th) order filter) and a high-pass filter cutofffrequency of approximately 130 kHz (as opposed to 25.875 kHz).$\begin{matrix}\begin{matrix}{{PSD}_{FBMsOL} = {K_{ADSL\_ OL} \times \frac{C}{f_{0}} \times \frac{\left\lbrack {\sin \left( {\pi \frac{f}{f_{0}}} \right)} \right\rbrack^{2}}{\left( {\pi \frac{f}{f_{0}}} \right)^{2}} \times}} \\{{~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~}{{\frac{1}{1 + \left( \frac{f}{f_{LP3dB}} \right)^{12}} \times \frac{1}{1 + \left( \frac{f_{HP3dB}}{f} \right)^{8}}},{0 \prec f \prec \infty}}}\end{matrix} & {{EQ}.\quad 4}\end{matrix}$

[0200] where PSD_(FBMsOL) represents the PSD mask, K_(ADSL) _(—) _(OL)represents a constant value, C represents a constant value, f representsa frequency of the downstream transmission, f₀ represents a constantvalue, f_(LP3dB) represents a 3 decibel (dB) low pass frequency andf_(HP3dB) represents a 3 dB high pass frequency. where PSD_(DBMsOL)represents the PSD mask, K_(ADSL) _(—) _(OL) represents a constantvalue, C represents a constant value, f represents a frequency of thedownstream transmission, f₀ represents a constant value, f_(LP3dB)represents a 3 decibel (dB) low pass frequency and f_(HP3dB) representsa 3 dB high pass frequency. K_(ADSL) _(—) _(OL) preferably has a valuebetween 0.0900 watts and 0.1200 watts and more preferably has a value of0.1104 watts. The constant f₀ preferably has a value between 2.100megahertz and 2.300 megahertz and more preferably has a value of 2.208megahertz. The constant f_(LP3dB) has a value substantially equal to$\frac{f_{0}}{2}.$

[0201] The constant f_(HP3dB) has preferably has a value between 27kilohertz and 40 kilohertz and more preferably has a value of 32kilohertz. The constant C preferably has a value between 0.1 and 10 andmore preferably has a value of 2.

[0202] HSDBM achieves its high performance by leveraging a combinationof DBM full overlap mask up to approximately 1.5 km and DBMsOL mask (aspectrally shaped version of DBMOL) up to approximately 2.0 km. TheDBMsOL mask is identical to that used for XOL and XDD systems of C.X.Within it's range of deployment, HSDBM is spectrally compatible with theFirst Group systems when deployed in the same quadrant. The HSDBM systemtherefore may be suitable for deployment up to 2 km with the First Groupsystems in the same quadrant.

[0203] In another embodiment of the present invention, a new Annex toG992.1 is defined based on existing G992.1 Annex C, for a 2.208megahertz (MHz) band ADSL extended spectrum that operates in the samecable bundle as TCM-ISDN. The following describes the changes to G992.1Annex C to support 512 subcarriers in downstream transmissions.

[0204] The current G.992.1 Annex C standard is currently supportsdownstream bandwidth of 1.104 MHz. In one embodiment of the presentinvention, the bandwidth preferably is extended to 2.208 MHz by definingNSC=512 as the number of downstream sub channels. All places in thecurrent G.991.1 Annex C standard which refers to the absolute number forthe downstream subchannels may be replaced by a function of NSC. Thefollowing illustrate such changes:

[0205] C.4.7.2 Data Subcarriers (Modifies 7.11.1.1)

[0206] The channel analysis signal defined in 10.6.6 allows for amaximum of NSC−1 carriers (at frequencies nΔf, n=1 to NSC−1) to be used.

[0207] C.4.7.3 Nyquist frequency (modifies 7.11.1.3)

[0208] The carrier at the Nyquist frequency (#NSC) may not be used foruser data and may be real valued; other possible uses are for furtherstudy.

[0209] C.4.7.4 Modulation by the Inverse Discrete Fourier Transform(Replaces 7.11.2)

[0210] The modulating transform defines the relationship between the2*NSC real values x_(n) and the Z_(i): $\begin{matrix}{x_{n} = {{\sum\limits_{i = 0}^{{2*{NSC}} - 1}\quad {{\exp \left( \frac{{j\pi}\quad n\quad i}{NSC} \right)}Z_{i}\quad {for}\quad n}} = {{0\quad {to}\quad 2*{NSC}} - 1}}} & {{EQ}.\quad 5}\end{matrix}$

[0211] The constellation encoder and gain scaling generate only NSC−1complex values of Z_(i). In order to generate real values of x_(n), theinput values (NSC−1 complex values plus zero at DC and one real valuefor Nyquist if used) may be augmented so that the vector Z has Hermitiansymmetry. That is,

Z _(i) =conj (Z′ _(2*NSC−i)) for i=NSC+1 to 2*NSC−1  EQ. 6

[0212] C.4.7.5 Synchronization Symbol (Modifies 7.11.3)

[0213] The synchronization symbol permits recovery of the frame boundaryafter micro-interruptions that might otherwise force retraining.

[0214] The data symbol rate, f_(symb)=4 kHz, the carrier separation,Δf=4.3125 kHz, and the IDFT size, N=2*NSC, are such that a cyclic prefixof {fraction (5/64)}*NSC samples could be used. That is,

(2+{fraction (5/64)})×NSC×4.0=2*NSC×4.3125

[0215] The cyclic prefix may, however, be shortened to ⅛*NSC samples,and a synchronization symbol (with a nominal length of (2+⅛)×NSCsamples) is inserted after every 68 data symbols. That is,

(2+⅛)×NSC×69=(2+{fraction (5/64)})×NSC×68

[0216] The data pattern used in the synchronization symbol may be thepseudo-random sequence PRD, (d_(n), for n=1 to 2*NSC) defined by:$\begin{matrix}\begin{matrix}{d_{n} = 1} & {for} & {n = {1\quad {to}\quad 9}} \\{d_{n} = {d_{n - 4} \oplus d_{n - 9}}} & {for} & {n = {10\quad {to}\quad 2*{NSC}}}\end{matrix} & {{EQ}.\quad 7}\end{matrix}$

[0217] The first pair of bits (d₁ and d₂) may be used for the DC andNyquist subcarriers (the power assigned to them is zero, so the bits areeffectively ignored); the first and second bits of subsequent pairs thenare used to define the X_(i) and Y_(i) for i=1 to NSC−1.

[0218] The period of the PRD is only 511 bits, so d₅₁₂ may be set beequal to d₁. The d₁-d₉ are re-initialized for each synchronizationsymbol, so each symbol uses the same data. The two bits that modulatethe pilot carrier, may be overwritten by {0,0}, thereby generating the{+,+} constellation.

[0219] The minimum set of subcarriers to be used is the set used fordata transmission (i.e. those for which b_(i)>0) which b_(i)=0 may beused at a reduced PSD is defined in transmit PSD-related portionsAnnexes A, B and C. The data modulated onto each subcarrier may be asdefined above; it may not depend on which subcarriers are used.

[0220] C.4.7.6 Cyclic Prefix (Replaces 7.12)

[0221] The last ⅛*NSC samples of the output of the IDFT (x_(n) forn=2*NSC−⅛*NSC to 2*NSC−1) may be prepended to the block of 2*NSC samplesand read out to the digital-to-analogue converter (DAC) in sequence. Forexample, when NSC=256, the subscripts, n, of the DAC samples in sequenceare 480 . . . 511, 0 . . . 511. The cyclic prefix may be used for allsymbols beginning with the C-RATES1 segment of the initializationsequence, as defined in 10.6.2.

[0222] C.7.4.4 C-REVERB1 (replaces 10.4.5)

[0223] C-REVERB1 is a signal that allows the ATU-C and ATU-R receiver toadjust its automatic gain control (AGC) to an appropriate level. Thedata pattern used in C-REVERB1 may be the pseudo-random downstreamsequence (PRD), d_(n) for n=1 to 2*NSC, defined in EQ.

[0224] 7.

[0225] The bits may be used as follows: the first pair of bits (d₁ andd₂) is used for the DC and Nyquist subcarriers (the power assigned tothem is, of course, zero, so the bits are effectively ignored); then thefirst and second bits of subsequent pairs are used to define the X_(i)and Y_(i) for i=1 to NSC−1 as defined in Table 7-13 of the G.992.1recommendation.

[0226] The period of PRD is only 511 bits, so d₅₁₂ may be set be equalto d₁. The bits d₁ to d₉ may be re-initialized for each symbol, so eachsymbol of C-REVERB1 is identical. The two bits that modulate the pilotcarrier may be overwritten by {0,0}, thus generating the {+,+}constellation.

[0227] The duration of C-REVERB1 is 512 (repeating) symbols withoutcyclic prefix. Note that when NSC=512 the PRD generally has to generate1024 bit which is two periods of the PRD. Since only the first period ofthe PRD is initialized with ones for n=1 to 9, the second period will becompletely random compared to the first period of the PRD there for the9 bit PRD generator is sufficient for generating the signals withNSC=512.

[0228] C.7.10.3 R-B&G (replaces 10.9.14)

[0229] The purpose of R-B&G is to transmit to ATU-C the bits and gainsinformation, Bitmap-F_(R) {b₁, g₁, b₂, g₂, . . . , b_(NSC−1),g_(NSC−1)}, and Bitmap-N_(R) {b_(NSC+1), g_(NSC+1), b_(NSC+2),g_(NSC+2), . . . , b_(2*NSC−1), g_(2*NSC−1)}, to be used on thedownstream subcarriers. In of Bitmap-F_(R) indicates the number of bitsto be coded by ATU-C transmitter onto the ith downstream subcarrier inFEXT_(R) symbols; g_(i) of Bitmap-F_(R) indicates the scale factor thatmay be applied to the ith downstream subcarrier in FEXT_(R) symbols,relative to the gain that was used for that carrier during thetransmission of C-MEDLEY. Similarly, b_(i) of Bitmap-N_(R) indicates thenumber of bits onto the (i−NSC)th downstream carrier in NEXT_(R)symbols; g_(i) of Bitmap-N_(R) indicates the scale factor that may beapplied to the (i−NSC)th downstream carrier in NEXTR symbols. Because nobits or energy will be transmitted at DC or one-half the sampling rate,b₀, g₀, b_(NSC), g_(NSC), b_(2*NSC), and g_(2*NSC) are all presumed tobe zero, and are not transmitted. Because subcarrier 64 is reserved asthe pilot tone, b₆₄ and b_(NSC+64), may be set to 0, g₆₄ and g_(NSC+64)may be set to g_(sync). The value g_(sync) represents the gain scalingapplied to the sync symbol.

[0230] The R-B&G information may be mapped in a (2*NSC−2)*16=16352-bit((2*NSC−2)*2=2044 byte) message m defined by: m={m_((2*NSC−2)*16-1),m_((2*NSC−2)*16-2), . . . , m₁, m₀}={g_(2*NSC−1), b_(2*NSC−1), . . . ,g_(NSC+1), b_(NSC+1), g_(NSC−1), b_(NSC−1), . . . , g₁, b₁}, with theMSB of b_(i) and g_(i) in the higher m index and m₀ being transmittedfirst. The message m may be transmitted in (2*NSC−2)*2=2044 symbols,using the transmission method as described in 10.9.8.

[0231] When Bitmap-N_(R) is disabled (FEXT Bitmap mode), b_(i) and g_(i)of Bitmap-N_(R) may be set to zero.

[0232] C.8.1.1 Bit Swap Request (Replaces 11.2.3)

[0233] The receiver may initiate a bit swap by sending a bit swaprequest to the transmitter via the AOC channel. This request informs thetransmitter which subcarriers are to be modified. The format of therequest is shown in Table C.8 of the G.992.1 specification (Table 7below). TABLE 7 Table C.8/G.992.1 - Format of the bit swap requestmessage Message header Message field 1-4 {11111111₂} Bitmap ExtensionCommand Subchannel (8 bits) index to (6 bits) index (8 (1 bit)Subchannel bits) index (1 bits)

[0234] The request comprises the nine bytes as follows:

[0235] an AOC message header consisting of 8 binary ones;

[0236] message fields 1-4, each of which consists of one-bit bitmapindex, a seven-bit command followed by a related eight-bit subchannelindex. One-bit bitmap index, a second bit is the extension to subchannelindex and valid six-bit commands for the bit swap message may be asshown in Table C.9. In Table C.9, the MSB for the bit swap requestcommand represents the Bitmap index. For downstream data, Bitmap indexequals 0 indicates Bitmap-FR, and Bitmap index equals 1 indicatesBitmap-NR. Similarly for upstream data, Bitmap index equals 0 indicatesBitmap-F_(C), and 1 indicates Bitmap-N_(C). The eight-bit subchannelindex is counted from low to high frequencies with the lowest frequencysubcarrier having the number zero. The subcarrier index zero may not beused.

[0237] the bit swap between FEXT_(C/R) symbols and NEXT_(C/R) symbols isnot allowed. TABLE 8 Table I.9/G.992.1 - Bit swap request command Value(8 bit) Interpretation yz000000₂ Do nothing yz000001₂ Increase thenumber of allocated bits by one yz000010₂ Decrease the number ofallocated bits by one yz000011₂ Increase the transmitted power by 1 dByz000100₂ Increase the transmitted power by 2 dB yz000101₂ Increase thetransmitted power by 3 dB yz000110₂ Reduce the transmitted power by 1 dByz000111₂ Reduce the transmitted power by 2 dB yz001xxx₂ Reserved forvendor discretionary commands

[0238] The bit swap request message (i.e. header and message fields) istransmitted five consecutive times. To avoid g_(i) divergence betweenATU-C and ATU-R after several bit swaps, for a g_(i) update of A dB thenew g_(i) value should be given by Equation 8:

g _(i)′=({fraction (1/512)})×round(512×g _(i)×10 exp(Δ/20))

[0239] C.7.10.1 R-MSG-RA (Supplements 10.9.2)

[0240] Replace Table 10-15 of the Recommendation with Table 9 below.TABLE 9 Table C.7/G.992.1 - Assignment of 80 bits of R-MSG-RA (Annex C)Suffix(ces) of m_(i) Parameter (Note) All reserved bits may be set to 079-69 Reserved for ITU-T 68 Extension to number of tones carrying data(included) 67-56 B_(fast-max) 55-49 Number of RS overhead bytes, (R)48-40 Number of RS payload bytes, K 39-32 Number of tones carrying data(ncloaded) 31-25 Estimated average loop attenuation 24-21 Coding gain20-16 Performance margin with selected rate option 15-14 Reserved forITU-T 13-12 Maximum Interleave Depth 11-0  Total number of bits per DMTsymbol, B_(max)

[0241] In accordance with yet another embodiment of the presentinvention, the spectral compatibility and performance of G.992.1 Annex Asystems operating with overlapped spectra (AOL) is described in theJapan access network. The benefit of the overlapped spectrum is theincrease in downstream performance when compared to the non-overlappedcase in Annex A. Spectral compatibility simulations, using a TTCcompliant simulator, show that systems implementing A.X using the fulloverlap mask defined in G.992.1 Annex A can be deployed up to 1.5 km andmaintain spectral compatibility with the First Group systems deployed inthe same quadrant. Systems deployed using a spectrally shaped overlapmask can be deployed up to 2.0 km and maintain spectral compatibilitywith First Group systems when deployed in the same quadrant. The shapedoverlap Annex A mask is identical to that used for XOL and XDD systemsfor C.X. This same shaped overlap mask is spectrally compatible withAnnex C DBM up to 4.5 km when deployed in the same quadrant. The familyof overlap and shaped overlap masks for Annex A are referred to as A.X.

[0242] Annex A systems using full overlap spectrum (AOL) may utilize aG.992.1 mode that allows significant rate increases, especially at smallranges where the upstream bandwidth may accommodate higher bit loading.AOL systems thus may be used for providing high speed Annex A in Japan(e.g., 12 Mbits/s rate services). Provided below are spectralcompatibility simulation results that show AOL systems to be spectrallycompatible with First Group systems in the Japan network when deployedin the same quadrant up to 1.5 km. First group systems are identified asAnnex A (non-overlapped mask), Annex C DBM, Annex C FBM and TCM-ISDN.With additional spectral shaping, the spectral compatibility with AnnexC FBM may be improved such that may be deployed up to 2 km in the samequad with First Group systems. The family of overlap and shaped overlapmasks for Annex A are referred to as A.X. Shaping may be optimizedwithin the TTC original criterion based on 24 interferers in the sameQuad, or within the field criterion based on only one intra-quadinterferer.

[0243] The current Annex AOL downstream spectral mask is defined inG.992.1, Annex A, section A1.2, and described here in FIG. 4 andEquation 9. The ADSL overlap mask extends the usual downstream bandwidthdown to the POTS band (25.875 KHz). Note that unless otherwise stated,the PSD mask associated with a spectrum management class, as defined inFIG. 4 above and Equation 9 below, preferably is equal to the PSDtemplate plus 3.5 dB. Equation 8 provides an explicit form of the ITUADSL_OL PSD template that matches the mask used for DBMOL downstreamtransmissions. Table 10 provides explicit attenuation and levels ofDBMOL downstream spectral mask. $\begin{matrix}\begin{matrix}\begin{matrix}{{PSD}_{{ADSL\_ OL},{{ds}\text{-}{Disturber}}} = {K_{{ADSL\_ OL},{ds}} \cdot \frac{2}{f_{0}} \cdot \frac{\left\lbrack {\sin \left( {\pi \frac{f}{f_{0}}} \right)} \right\rbrack^{2}}{\left( {\pi \frac{f}{f_{0}}} \right)^{2}} \cdot}} \\{{~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~}{{\frac{1}{1 + \left( \frac{f}{f_{LP3dB}} \right)^{12}} \cdot \frac{1}{1 + \left( \frac{f_{HP3dB}}{f} \right)^{8}}},{0 \prec f \prec \infty}}}\end{matrix} \\{f{\text{:}\quad\lbrack{Hz}\rbrack}} \\{{f_{0} = {2.208 \times {10^{6}\quad\lbrack{Hz}\rbrack}}},{f_{LP3dB} = {\frac{f_{0}}{2}\left( {G{.992}{.1}} \right)}},} \\{{f_{HP3dB} = {25.875 \times {10^{3}\quad\lbrack{Hz}\rbrack}}},{K_{{ADSL\_ OL},{ds}} = {0.1104\quad\lbrack W\rbrack}}}\end{matrix} & {{EQ}.\quad 9}\end{matrix}$

TABLE 10 Frequency f(KHz) PSD (dBm/Hz) Peak values 0 < f < 4 −97.5dBm/Hz peak    4 < f < 25.875 −92.5 + 21 log₂(f/4) 25.875 < f < 1104  −36.5 dBm/Hz peak 1104 < f < 3093 −36.5 − 36 log₂(f/1104) 3093 < f    −90 dBm/Hz

[0244] The Annex A shaped overlap (AsOL) mask is defined by Equation 10below. Note that this preferably is the same shaped overlap mask asdefined for XOL and XDD systems. $\begin{matrix}{{{{PSD}_{{AsOL},{{ds} - {Disturber}}} = {K_{{ADSL\_ OL},{ds}} \cdot \frac{2}{f_{0}} \cdot \frac{\left\lbrack {\sin \left( {\pi \quad \frac{f}{f_{0}}} \right)} \right\rbrack^{2}}{\left( {\pi \quad \frac{f}{f_{0}}} \right)^{2}} \cdot \frac{1}{1 + \left( \frac{f}{f_{LP3dB}} \right)^{12}} \cdot \frac{1}{1 + \left( \frac{f_{HP3dB}}{f} \right)^{6}}}},{0 \prec f \prec \infty}}{f{\text{:}\quad\lbrack{Hz}\rbrack}}{{f_{0} = {2.208 \times {10^{6}\quad\lbrack{Hz}\rbrack}}},{f_{LP3dB} = {\frac{f_{0}}{2}\left( {G{.992}{.1}} \right)}},{f_{HP3dB} = {130 \times {10^{3}\quad\lbrack{Hz}\rbrack}}},{K_{{ADSL\_ OL},{ds}} = {0.1104\quad\lbrack W\rbrack}}}} & {{EQ}.\quad 10}\end{matrix}$

[0245] A.X Spectral Compatibility Results:

[0246] Spectral Compatibility Scenario 1: 24 Intra-Quad Interferers(A.X₂₄):

[0247] The spectral compatibility simulations were done according to TTCspecifications (TTC standard JJ10001) and the SEI contributionT465-9-13. Table 11 (FIG. 5) and Table 12 (FIG. 6) depict the spectralcompatibility of the A.X systems into First Group systems when a 24Intra-Quad Interferers are assumed. Note that for loop distances up to1.5 km the AOL mask preferably is used; for distances greater than 1.5km, the AsOL mask preferably is used. The entries in Tables 11 and 12are bit rates expressed in kbps for various 0.4 mm paper Japanese loops.Table 11 and 11 respectively show the spectral compatibility of A.X withFirst Group systems operating in G992.1 (full rate) and G992.2 (lite)modes. TCM-ISDN values are identical in both modes. The shaded columnsrefer to the reference values as given in the SEI contribution T465-9-13(Table 2). The white columns refer to the spectral compatibility of theA.X₂₄. The light shaded entries underline the failure to ensure thespectral compatibility.

[0248] The results of Tables 11 and 12 show that AOL is spectrallycompatible with First Group systems when deployed in the same quad up to1.5 km. AsOL is spectrally compatible with First Group systems whendeployed in the same quad up to 2.0 km. Spectral compatibility is thisrespect is defined where the computed bit rate is equal to or greaterthan the performance reference value.

[0249] Spectral Compatibility Scenario 2:1 Intra-Quad Interferer (A.X₁):

[0250] Table 13 (FIG. 7) depicts the spectral compatibility of the A.Xinto First Group systems for the case when Intra-Quad Interferer isassumed (A.X₁). Note that for loop distances up to 1.5 km the AOL maskis used; for distances greater than 1.5 km, the AsOL mask is used. Allthe values in Table 12 are expressed in kbps for 0.4 mm paper Japaneseloops. Table 13 shows the spectral compatibility of A.X with First Groupsystems operating in G992.1 (full rate) mode. The dark shaded columnsrefer to the reference values as given in Table 2 of the SEIcontribution T465-9-13. The white columns refer to the spectralcompatibility of the A.X₁. The light shaded entries underline thefailure to ensure the spectral compatibility. The results of Table 13show that AsOL is spectrally compatible with First Group systems whendeployed in the same quadrant up to 4.25 km.

[0251] The reach of Annex A with shaped spectral overlap (AsOL)typically is limited by TCM-ISDN to a maximum distance of about 3.5 km.When deployed up to 3.5 km, AsOL is spectrally compatible with thedownstream channels of all the First Group systems. In the presence of24 intra-quad crosstalk disturbers from AsOL, Annex C FBM has a verysmall degradation in bit rate relative to the performance referencevalue. The quality of service in the upstream channel Annex C FBM at adistance of 3.25 km is 192 kilobits per second (kb/s), which is ofrelatively satisfactory quality when considering the absolute value ofthe service. If the ratio of downstream channel bit rate to the upstreamchannel bit rate (see Table 14 below) is considered, it can be observedthat the ratios for the computed Annex C FBM values are comparable tothose of the performance reference values for CDBM and Annex A. Giventhat there is only a small deviation from the performance referencevalue of Annex C FBM mode, consideration should be given to allowdeployment of AsOL systems up to is the performance limiting bound of3.5 km. TABLE 14 Ratios of downstream bit rate to upstream bit rate. A992.1 CDBM992.1 CFBM992.1 Ref table Ref table Ref table 6.8 8.1 7.3 8.18.7 8.7 4.8 7.9 6.0 7.9 8.4 8.4 3.0 7.4 4.8 7.4 7.9 7.9 2.0 7.2 4.1 7.27.7 7.7 1.4 7.3 3.8 7.3 7.4 7.4 1.0 6.9 3.5 6.9 7.1 7.1 0.7 6.9 3.3 6.96.8 6.8 0.4 6.7 3.1 6.7 6.2 7.0 0.2 6.0 2.9 6.0 5.3 6.0 0.1 5.1 2.5 5.14.9 5.6 0.0 4.6 2.3 4.6 4.0 4.6 0.0 3.9 2.1 3.9 3.3 4.3 0.0 3.5 1.9 3.52.9 3.3 0.0 3.1 1.6 3.1 2.3 3.2 0.0 2.5 1.3 2.5 1.7 2.4 0.0 1.9 1.2 1.91.3 2.0 0.0 1.4 0.9 1.4 0.8 1.3 0.0 0.9 0.7 0.9 0.5 1.0 0.0 0.4 0.4 0.40.2 0.3

[0252] The experimental set up is the following: the bit procedureallocation limits the number of allocated bits to fourteen and does notconsider any loading below two bits. The coding gain provided by thechannel coding scheme is equal to 5 dB. No echo impairment is assumed.

[0253] A.X₂₄, AOL & Annex A (24 Intra-Quad Interferers scenario):

[0254] Table 15 shows the performances of Annex A, AOL, and A.X₂₄ in thepresence of −140 dBm/Hz background noise. Note that A.X₂₄ represents theuse of mask AOL for loop distances up to 1.5 km and mask AxOL fordistances greater than 1.5 km.

[0255] Table 16 shows the performances of Annex A, AOL, and A.X₂₄ in thepresence of worst case 24 disturber First Group systems. Note that A.X₂₄represents the use of mask AOL for loop distances up to 1.5 km and maskAxOL for distances greater than 1.5 km. TABLE 15 loop (km) A AOL A.X₂₄0.5 12416 13920 13920 0.75 12416 13920 13920 1 12416 13920 13920 1.2512384 13888 13888 1.5 11936 13440 13440 1.75 11072 12608 12576 2 995211456 11424

[0256] TABLE 16 loop (km) A AOL A.X₂₄ 0.5 7360 8576 8576 0.75 6400 74567456 1 4768 5728 5728 1.25 3168 4064 4064 1.5 2048 2848 2848 1.75 13442048 1504 2 736 1344 768

[0257] A.X₁ & Annex A (1 Intra-Quad Interferers scenario):

[0258] Table 17 shows typical performances of Annex A and AOL in thepresence of −140 dBm/Hz background noise. Table 18 shows typicalperformances of Annex A and AOL in the presence of worst case 24disturber First Group systems. Note that A.X1 is the same as AOL. TABLE17 Performance of AOL &Annex A in AWGN noise environment. loop (km) AA.X₁ 0.5 12416 13920 0.75 12416 13920 1 12416 13920 1.25 12384 13888 1.511936 13440 1.75 11072 12608 2 9952 11456

[0259] TABLE 18 Performance of A.X₁ &Annex A in First Group noiseenvironment. loop (km) A A.X₁ 0.5 9760 11232 0.75 8608 9920 1 7040 82561.25 5440 6592 1.5 3776 4864 1.75 2656 3648 2 1728 2624

[0260] Spectral compatibility simulations, using a TTC compliantsimulator, have shown that systems implementing A.X using the fulloverlap mask defined in G.992.1 Annex A can be deployed up to 1.5 km andmaintain spectral compatibility with the First Group systems deployed inthe same quadrant. Systems deployed using a spectrally shaped overlapmask can be deployed up to 2.0 km and maintain spectral compatibilitywith First Group systems when deployed in the same quadrant. The shapedoverlap Annex A mask is identical to that used for XOL and XDD systemsfor C.X. This same shaped overlap mask is spectrally compatible withAnnex C DBM up to 4.5 km when deployed in the same quadrant. The familyof overlap and shaped overlap masks for Annex A are herein referred toas A.X.

[0261] Method and System for Extended ADSL Downstream Spectrum and Ratein G.992.1 and Annexes:

[0262] The method and system described below relates to providingenhanced performance in extending downstream spectrum compliance andcompatibility and enhanced data rate in G.992.1 and annexesapplications, such as DSL. Specifically, the method and system providefor 2.208 MHz band ADSL extended spectrum that operates in the samecable bundle as TCM-ISDN. At least one embodiment of the presentinvention provides an arrangement to enable G992.1 Annex C to support512 subcarriers in downstream.

[0263] G.dmt Annex C standard currently supports downstream bandwidth of1.104 MHz. The present invention provides for the extension of thebandwidth to 2.208 MHz by defining NSC=512 as the number of downstreamsub channels. In considering the present state of the G.992.1 Annex C,all references to the absolute number for the downstream sub channelsmay be optimally replaced by a function of NSC as set forth below. Forinstance, one could replace all references in Annex C to the absolutenumber for the downstream sub channels with the function of NSC asdetailed below:

[0264] Data Subcarriers (Modifies 7.11.1.1—of G.992.1)

[0265] The channel analysis signal defined in 10.6.6 allows for amaximum of NSC−1 carriers (at frequencies nΔf, n=1 to NSC−1) to be used.

[0266] Nyquist Frequency (Modifies 7.11.1.3)

[0267] The carrier at the Nyquist frequency (#NSC) preferably is not beused for user data and may be real valued; other possible uses are forfurther study.

[0268] Modulation by the Inverse Discrete Fourier Transform (Replaces7.11.2)

[0269] The modulating transform defines the relationship between the2*NSC real values x_(n) and the Z_(i): $\begin{matrix}\begin{matrix}{x_{n} = {\sum\limits_{i = 0}^{{2*{NSC}} - 1}{{\exp \left( \frac{j\quad \pi \quad n\quad i}{NSC} \right)}Z_{i}}}} & \quad & {{{for}\quad n} = {{0\quad {to}\quad 2*{NSC}} - 1}}\end{matrix} & {{EQ}.\quad 11}\end{matrix}$

[0270] The constellation encoder and gain scaling generate only NSC−1complex values of Z_(i). In order to generate real values of x_(n), theinput values (NSC−1 complex values plus zero at DC and one real valuefor Nyquist if used) may be augmented so that the vector Z has Hermitiansymmetry. That is,

Z _(i) =conj (Z′ _(2*NSC−i)) for i=NSC+1 to 2*NSC−1  EQ. 12

[0271] Synchronization Symbol (Modifies 7.11.3)

[0272] The synchronization symbol permits recovery of the frame boundaryafter micro-interruptions that might otherwise force retraining.

[0273] The data symbol rate, f_(symb)=4 kHz, the carrier separation,Δf=4.3125 kHz, and the IDFT size, N=2*NSC, are such that a cyclic prefixof {fraction (5/64)}*NSC samples could be used. That is,

(2+{fraction (5/64)})×NSC×4.0=2*NSC×4.3125  EQ. 13

[0274] The cyclic prefix, however, is shortened to ⅛*NSC samples, and asynchronization symbol (with a nominal length of (2+⅛)×NSC samples) isinserted after every 68 data symbols. That is,

(2+⅛)×NSC×69=(2+{fraction (5/64)})×NSC×68  EQ. 14

[0275] The data pattern used in the synchronization symbol is thepseudo-random sequence PRD, (d_(n), for n=1 to 2*NSC) defined by:$\begin{matrix}\begin{matrix}{d_{n} = 1} & {{{for}\quad n} = {1\quad {to}\quad 9}} \\{d_{n} = {d_{n - 4} \oplus d_{n - 9}}} & {{{for}\quad n} = {10\quad {to}\quad 2*{NSC}}}\end{matrix} & {{EQ}.\quad 15}\end{matrix}$

[0276] The first pair of bits (d₁ and d₂) may be used for the DC andNyquist subcarriers (the power assigned to them is zero, so the bits areeffectively ignored); the first and second bits of subsequent pairs arethen used to define the X_(i) and Y_(i) for i=1 to NSC−1 as shown inTable 7-13 of G.992.1.

[0277] The period of the PRD is only 511 bits, so d₅₁₂ maybe equal tod₁. The d₁-d₉ may be re-initialized for each synchronization symbol, soeach symbol uses the same data. The two bits that modulate the pilotcarrier, may be overwritten by {0,0}: generating the {+,+}constellation.

[0278] The minimum set of subcarriers to be used is the set used fordata transmission (i.e. those for which b_(i)>0); subcarriers for whichb_(i)=0 may be used at a reduced. PSD as defined in transmit PSDparagraphs of Annexes A, B and C. The data modulated onto eachsubcarrier may be as defined above; it may not depend on whichsubcarriers are used.

[0279] Cyclic Prefix (Replaces 7.12)

[0280] The last ⅛*NSC samples of the output of the IDFT (x_(N) forn=2*NSC−⅛*NSC to 2*NSC−1) may be prepended to the block of 2*NSC samplesand read out to the digital-to-analogue converter (DAC) in sequence. Forexample, when NSC=256, the subscripts, n, of the DAC samples in sequenceare 480 . . . 511, 0 . . . 511.

[0281] The cyclic prefix may be used for all symbols beginning with theC-RATES1 segment of the initialization sequence, as defined in 10.6.2.

[0282] C-REVERB1 (Replaces 10.4.5)

[0283] C-REVERB1 is a signal that allows the ATU-C and ATU-R receiver toadjust its automatic gain control (AGC) to an appropriate level. Thedata pattern used in C-REVERB1 may be the pseudo-random downstreamsequence (PRD), d_(n) for n=1 to 2*NSC, defined in 7.11.3 and repeatedhere for convenience:

[0284] d_(n)=1 for n=to 9

[0285] d_(n)=d_(n−4)⊕d_(n−9) for n=10 to 2*NSC

[0286] The bits may be used as follows: the first pair of bits (d₁ andd₂) is used for the DC and Nyquist subcarriers (the power assigned tothem is, of course, zero, so the bits are effectively ignored); then thefirst and second bits of subsequent pairs are used to define the X_(i)and Y_(i) for i=1 to NSC−1 as defined in Table 7-13 of G.992.1. Theperiod of PRD is only 511 bits, so d₅₁₂ may be equal to d₁. The bits d₁to d₉ may be re-initialized for each symbol, so each symbol of C-REVERB1is identical.

[0287] The two bits that modulate the pilot carrier may be overwrittenby {0,0}: generating the {+,+} constellation.

[0288] The duration of C-REVERB1 is 512 (repeating) symbols withoutcyclic prefix.

[0289] Note: When NSC=512, the PRD has to generate 1024 bit which is twoperiods of the PRD. Since only the first period of the PRD is initializewith ones for n=1 to 9 the second period will be completely randomcompare to the first period of the PRD there for the 9 bit PRD generatoris sufficient for generating the signals with NSC=512.

[0290] R-B&G (Replaces 10.9.14)

[0291] The purpose of R-B&G is to transmit to ATU-C the bits and gainsinformation, Bitmap-F_(R) {b₁, g₁, b₂; g₂, . . . , b_(NSC−1),g_(NSC−1)}, and Bitmap-NR {b_(NSC+1), g_(NSC+1), b_(NSC+2), g_(NSC+2), .. . , b_(2*NSC−1), g_(2*NSC-1)}, to be used on the downstreamsubcarriers. b_(i) of Bitmap-F_(R) indicates the number of bits to becoded by ATU-C transmitter onto the ith downstream subcarrier inFEXT_(R) symbols; g_(i) of Bitmap-F_(R) indicates the scale factor thatmay be applied to the ith downstream subcarrier in FEXT_(R) symbols,relative to the gain that was used for that carrier during thetransmission of C-MEDLEY. Similarly, b_(i) of Bitmap-N_(R) indicates thenumber of bits onto the (i−NSC)th downstream carrier in NEXT_(R)symbols; g_(i) of Bitmap-N_(R) indicates the scale factor that may beapplied to the (i−NSC)th downstream carrier in NEXT_(R) symbols. Becauseno bits or energy will be transmitted at DC or one-half the samplingrate, b₀, g₀, b_(NSC), g_(NSC), b_(2*NSC), and g_(2*NSC) are allpresumed to be zero, and are not transmitted. Because subcarrier 64 isreserved as the pilot tone, b₆₄ and b_(NSC+64), may be set to 0, g₆₄ andg_(NSC+64) may be set to g_(sync). The value g_(sync) represents thegain scaling applied to the sync symbol.

[0292] The R-B&G information may be mapped in a (2*NSC−2)*16=16352-bit((2*NSC−2)*2=2044 byte) message m defined by:

m={m_((2*NSC−2)*16-1), m_((2*NSC−2)*16-2) , . . . , m ₁,m₀}={g_(2*NSC−1), b_(2*NSC−1), . . . , g_(NSC+1), b_(NSC+1), g_(NSC−1),b_(NSC−1), g₁, b₁}  EQ. 16

[0293] with the MSB of b_(i) and g_(i) in the higher m index and m₀being transmitted first. The message m may be transmitted in(2*NSC−2)*2=2044 symbols, using the transmission method as described in10.9.8. When Bitmap-N_(R) is disabled (FEXT Bitmap mode), b_(i) andg_(i) of Bitmap-N_(R) may be set to zero.

[0294] One aspect to this is AOC online adaptation and reconfiguration.Bit swap request (replaces 11.2.3), is addressed as follows. Thereceiver initiates a bit swap by sending a bit swap request to thetransmitter via the AOC channel. This request tells the transmitterwhich subcarriers are to be modified. The format of the request is shownin Table 19. TABLE 19 G.992.1 - Format of the bit swap request messageMessage header Message field 1-4 {11111111₂} Bitmap Extension CommandSubchannel (8 bits) index to (6 bits) index (8 (1 bit) Subchannel bits)index (1 bits)

[0295] The request may comprise nine bytes as follows:

[0296] an AOC message header consisting of 8 binary ones;

[0297] message fields 1-4, each of which consists of one-bit bitmapindex, a seven-bit command followed by a related eight-bit subchannelindex. One-bit bitmap index, a second bit is the extension to subchannelindex and valid six-bit commands for the bit swap message may be asshown in Table 24. In Table 24, the MSB for the bit swap request commandrepresents the Bitmap index. For downstream data, that the Bitmap indexequals 0 indicates Bitmap-FR, and Bitmap index equals 1 indicatesBitmap-NR. Similarly for upstream data, Bitmap index equals 0 indicatesBitmap-F_(C), and 1 indicates Bitmap-N_(C). The eight-bit subchannelindex is counted from low to high frequencies with the lowest frequencysubcarrier having the number zero. The subcarrier index zero may not beused.

[0298] the bit swap between FEXT_(C/R) symbols and NEXT_(C/R) symbols isnot allowed. TABLE 20 G.992.1 - Bit swap request command Value (8 bit)Interpretation yz000000₂ Do nothing yz000001₂ Increase the number ofallocated bits by one yz000010₂ Decrease the number of allocated bits byone yz000011₂ Increase the transmitted power by 1 dB yz000100₂ Increasethe transmitted power by 2 dB yz000101₂ Increase the transmitted powerby 3 dB yz000110₂ Reduce the transmitted power by 1 dB yz000111₂ Reducethe transmitted power by 2 dB yz001xxx₂ Reserved for vendordiscretionary commands

[0299] The bit swap request message (i.e. header and message fields) maybe transmitted five consecutive times. To avoid g_(i) divergence betweenATU-C and ATU-R after several bit swaps, for a g_(i) update of Δ dB thenew g_(i) value should be given by:

g _(i)′=({fraction (1/512)})×round(512×g _(i)×10 exp(Δ/20))

[0300] Modifying R-MSG-RA exchange state supports up to 511 tonescarrying data and maximum rate supported for dual latency increased to24480 Kbps.

[0301] R-MSG-RA (Supplements 10.9.2)

[0302] Replace Table 10-15 with Table 21. TABLE 21 G.992.1 - Assignmentof 80 bits of R-MSG-RA (Annex C) Suffix(ces) of m_(i) Parameter (Note)All reserved bits may be set to 0 79-69 Reserved for ITU-T 68 Extensionto number of tones carrying data (ncloaded) 67-56 B_(fast-max) 55-49Number of RS overhead bytes, (R) 48-40 Number of RS payload bytes, K39-32 Number of tones carrying data (ncloaded) 31-25 Estimated averageloop attenuation 24-21 Coding gain 20-16 Performance margin withselected rate option 15-14 Reserved for ITU-T 13-12 Maximum InterleaveDepth 11-0  Total number of bits per DMT symbol, B_(max)

[0303] The embodiment of the present invention as described aboveprovides necessary changes to Annex C to G992.1, for ADSL extendedspectrum that will cover 2.208 MHz band, and will operate in the samecable bundle as TCM-ISDN.

[0304] Based on the suggested changes to Annex C to G992.1 for 2.208MHz, ADSL extended spectrum that operates in the same cable bundle asTCM-ISDN allows overlap mode of operation between downstream andupstream. This aspect of the present invention provides performance gainthat can be achieved for downstream rates when using overlapped mode ofoperation as compared to non-overlapped mode. The overlapped mode ofoperation is part of the suggested 2.208 MHz ADSL extended spectrum thatoperates in the same cable bundle as TCM-ISDN.

[0305] To establish the performance gain of the invention, simulationswere run for 2.208 MHz bandwidth system using DBM mode with thefollowing configuration parameters:

[0306] ADSL+ PSD Mask:

[0307] The use of the ADSL+ overlapped mode PSD mask for CO deploymentof FIG. 8

[0308] Total power: 21.25 dBm

[0309] Margin=6 dB

[0310] SNR Gap=9.75 dB

[0311] Coding gain=5 dB (assuming Trellis+RS coding)

[0312] White noise power=−140 dBm/Hz

[0313] 0.4 mm paper cable loop

[0314] Noise: 24 TCM ISDN noise+20 SELF NEXT+20 SELF FEXT

[0315] Start bin for overlapped mode −6

[0316] Start bin for overlapped mode −32

[0317] Dual bit map calculation method: Cfext*126/340+Cnext*214/340

[0318]FIG. 9 illustrates the performance of 2.208 MHz band ADSL extendedspectrum operating in the same bundle as TCM-ISDN. As can be seen fromFIG. 9, the overlapped mode improves the system performance, in thedownstream direction by at least 1 Mbps.

[0319] PSD Mask for ADSL+:

[0320] Another aspect of the present invention provides a PSD mask foruse in ADSL+ assuming an implementation with 512 carriers. In oneembodiment, PSD masks are used for operation over POTS and over ISDN. Inaddition, a PSD for CO deployments and a separate PSD for remoteterminal deployments may be employed. This inventive embodimentcontemplates PSD mask definitions for use in ADSL+ assuming animplementation with 512 carriers. In addition, the present inventionuses definition of separate PSD masks for CO deployments and remoteterminal deployments.

[0321] For ADSL+ operation over POTS, a mask is defined with thedownstream mask overlapped with the upstream and a non-overlapped mask.Further overlapped and non-overlapped masks are defined for centraloffice deployments and for remote terminal deployments. Further masksfor ADSL+ operation over POTS are defined.

[0322] For ADSL+ operation over ISDN, non-overlapped masks arepreferred. As with ADSL over POTS, a mask for deployment from the CO andanother for deployment from the cabinet.

[0323] ADSL+ Over POTS PSD:

[0324] PSD masks for ADSL+ operation over POTS are defined in thefollowing. Note that in these cases, the corresponding template is 3.5dB lower than the mask. Masks are defined for overlap mode,non-overlapped (FDM) mode, CO deployment, and Cabinet deployment.

[0325] Deployment from CO:

[0326] With ADSL+ deployed from the CO, the PSD mask follows that of COMask 2 from T1.424/Trial-Use up to the maximum in band frequency of2.208 MHz. Table 22 lists the preferred approximate breakpoints for theoverlapped ADSL+ PSD Mask for CO deployment derived from CO Mask 2 ofT1.424/Trial-Use. The mask is plotted in FIG. 10. The maximum power forthis mode of operation may be established, it may be fixed or adaptivelydetermined.

[0327] Table 23 lists the preferred approximate breakpoints for thenon-overlapped ADSL+ PSD Mask for CO deployment. The mask is plotted inFIG. 11. The maximum power for this mode of operation may beestablished, it may be fixed or it may be adaptively determined. TABLE22 ADSL+ Over POTS PSD for CO Deployment (Overlap Mode) Frequency (kHz)Mask (dBm/Hz) 0 −97.5 4 −97.5 4 −92.5 25 −36.5 1104 −36.5 2208 −46.539.25 −101.5 8500 −101.5 8500 −103.5 11040 −103.5

[0328] TABLE 23 ADSL+ Over POTS PSD for CO Deployment (Non-overlappedMode) Frequency (kHz) Mask (dBm/Hz) 0 −97.5 4 −97.5 80 −72.5 138 −36.51104 −36.5 2208 −46.5 39.25 −101.5 8500 −101.5 8500 −103.5 11040 −103.5

[0329] Deployment from the Cabinet

[0330] When ADSL+ is deployed from a Cabinet, the PSD preferably followsthat of Cabinet Mask 2 from T1.424/Trial-Use up to the maximum in bandfrequency of 2.208 MHz.

[0331] Table 24 lists the preferred approximate breakpoints for theoverlapped ADSL+ PSD Mask for Cabinet deployment. The corresponding PSDmask is plotted in FIG. 12. The maximum power for this mode of operationmay be established, it may be fixed or it may be adaptively determined.

[0332] Table 25 lists the preferred approximate breakpoints for thenon-overlapped ADSL+ PSD Mask for Cabinet deployment operating. The maskis plotted in FIG. 13. The maximum power for this mode of operation maybe established, it may be fixed or it may be adaptively determined.TABLE 24 ADSL+ over POTS PSD for Cabinet Deployment (Overlapped Mode)Frequency (kHz) Mask (dBm/Hz) 0 −97.5 4 −97.5 4 −92.5 25 −56.5 1104−56.5 2208 −46.5 39.25 −101.5 8500 −101.5 8500 −103.5 11040 −103.5

[0333] TABLE 25 ADSL+ over POTS PSD for Cabinet Deployment(Non-overlapped Mode) Frequency (kHz) Mask (dBm/Hz) 0 −97.5 4 −97.5 80−72.5 138 −56.5 1104 −56.5 2208 −46.5 39.25 −101.5 8500 −101.5 8500−103.5 11040 −103.5

[0334] ADSL+ over ISDN:

[0335] Deployment from CO:

[0336] Table 26 lists the preferred approximate breakpoints for theoverlapped ADSL+ over ISDN PSD Mask for Central Office deployment. ThisPSD mask is plotted in FIG. 14. The maximum power for this mode ofoperation may be established, it may be fixed or it may be adaptivelydetermined. TABLE 26 ADSL+ Over ISDN PSD for CO Deployment Frequency(kHz) Mask (dBm/Hz) 0 −90 93.1 −90 209 −62 255 −36.5 1104 −36.5 2208−46.5 39.25 −101.5 8500 −101.5 8500 −103.5 11040 −103.5

[0337] Deployment from the Cabinet

[0338] Table 27 lists the preferred approximate breakpoints for thenon-overlapped ADSL+ over ISDN PSD Mask for Cabinet deploymentoperating. The mask is plotted in FIG. 15. The maximum power for thismode of operation may be established, it may be fixed or it may beadaptively determined. TABLE 27 ADSL+ over ISDN PSD for CabinetDeployment Frequency (kHz) Mask (dBm/Hz) 0 −90 93.1 −90 209 −62 254−56.5 1104 −56.5 2208 −46.5 39.25 −101.5 8500 −101.5 8500 −103.5 11040−103.5

[0339] In keeping with this embodiment of the present invention, thefollowing PSD Masks defined above for ADSL+ for the different deploymentscenarios may be adopted:

[0340] ADSL over POTS with overlapping upstream and downstream spectradeployed from the CO

[0341] ADSL over POTS with non-overlapping upstream and downstreamspectra deployed from the CO

[0342] ADSL over POTS with overlapping upstream and downstream spectradeployed from the Cabinet

[0343] ADSL over POTS with non-overlapping upstream and downstreamspectra deployed from the Cabinet

[0344] ADSL over ISDN with non-overlapping upstream and downstreamspectra deployed from the CO

[0345] ADSL over ISDN with non-overlapping upstream and downstreamspectra deployed from the Cabinet

[0346] To summarize:

[0347] In accordance with one embodiment of the present invention, apower spectral density (PSD) mask for spectral shaping of anasynchronous digital subscriber line (ADSL) overlap spectrumtransmission over a plain old telephone system (POTS) is provided. ThePSD mask is represented at least in part by a plurality of break points,the plurality of break points including:

[0348] approximately −97.5 decibel-milliwatts per hertz (dBm/Hz) atapproximately 0 kilohertz (kHz);

[0349] approximately −97.5 dBm/Hz at approximately 4 kHz;

[0350] approximately −92.5 dBm/Hz at approximately 4 kHz;

[0351] approximately −36.5 dBm/Hz at approximately 25 kHz;

[0352] approximately −36.5 dBm/Hz at approximately 1104 kHz;

[0353] approximately −46.5 dBm/Hz at approximately 2208 kHz;

[0354] approximately −101.5 dBm/Hz at approximately 39.25 kHz;

[0355] approximately −101.5 dBm/Hz at approximately 8500 kHz;

[0356] approximately −103.5 dBm/Hz at approximately 8500 kHz; and

[0357] approximately −103.5 dBm/Hz at approximately 11040 kHz.

[0358] In accordance with another embodiment of the present invention, apower spectral density (PSD) mask for spectral shaping of anasynchronous digital subscriber line (ADSL) non-overlap spectrum over aplain old telephone system (POTS) is provided. The PSD mask may berepresented at least in part by a plurality of break points, theplurality of break points including:

[0359] approximately −97.5 decibel-milliwatts per hertz (dBm/Hz) atapproximately 0 kilohertz (kHz);

[0360] approximately −97.5 dBm/Hz at approximately 4 kHz;

[0361] approximately −72.5 dBm/Hz at approximately 80 kHz;

[0362] approximately −36.5 dBm/Hz at approximately 138 kHz;

[0363] approximately −36.5 dBm/Hz at approximately 1104 kHz;

[0364] approximately −46.5 dBm/Hz at approximately 2208 kHz;

[0365] approximately −101.5 dBm/Hz at approximately 3925 kHz;

[0366] approximately −101.5 dBm/Hz at approximately 8500 kHz;

[0367] approximately −103.5 dBm/Hz at approximately 8500 kHz; and

[0368] approximately −103.5 dBm/Hz at approximately 11040 kHz.

[0369] In accordance with an additional embodiment of the presentinvention, a power spectral density (PSD) mask for spectral shaping ofan asynchronous digital subscriber line (ADSL) overlap spectrum over aplain old telephone system (POTS) is provided. The PSD mask may berepresented at least in part by a plurality of break points, theplurality of break points including:

[0370] approximately −97.5 decibel-milliwatts per hertz (dBm/Hz) atapproximately 0 kilohertz (kHz);

[0371] approximately −97.5 dBm/Hz at approximately 4 kHz;

[0372] approximately −92.5 dBm/Hz at approximately 4 kHz;

[0373] approximately −56.5 dBm/Hz at approximately 25 kHz;

[0374] approximately −56.5 dBm/Hz at approximately 1104 kHz;

[0375] approximately −46.5 dBm/Hz at approximately 2208 kHz;

[0376] approximately −101.5 dBm/Hz at approximately 3925 kHz;

[0377] approximately −101.5 dBm/Hz at approximately 8500 kHz;

[0378] approximately −103.5 dBm/Hz at approximately 8500 kHz; and

[0379] approximately −103.5 dBm/Hz at approximately 11040 kHz.

[0380] In accordance with another embodiment of the present invention, apower spectral density (PSD) mask for spectral shaping of anasynchronous digital subscriber line (ADSL) non-overlap spectrum over aplain old telephone system (POTS) is provided. The PSD mask may berepresented at least in part by a plurality of break points, theplurality of break points including:

[0381] approximately −97.5 decibel-milliwatts per hertz (dBm/Hz) atapproximately 0 kilohertz (kHz);

[0382] approximately −97.5 dBm/Hz at approximately 4 kHz;

[0383] approximately −92.5 dBm/Hz at approximately 80 kHz;

[0384] approximately −56.5 dBm/Hz at approximately 138 kHz;

[0385] approximately −56.5 dBm/Hz at approximately 1104 kHz;

[0386] approximately −46.5 dBm/Hz at approximately 2208 kHz;

[0387] approximately −101.5 dBm/Hz at approximately 3925 kHz;

[0388] approximately −101.5 dBm/Hz at approximately 8500 kHz;

[0389] approximately −103.5 dBm/Hz at approximately 8500 kHz; and

[0390] approximately −103.5 dBm/Hz at approximately 11040 kHz.

[0391] In accordance with yet another embodiment of the presentinvention, a power spectral density (PSD) mask for spectral shaping ofan asynchronous digital subscriber line (ADSL) overlap spectrum over anintegrated digital services network (ISDN) is provided. The PSD mask maybe represented at least in part by a plurality of break points, theplurality of break points including:

[0392] approximately −90 decibel-milliwatts per hertz (dBm/Hz) atapproximately 0 kilohertz. (kHz);

[0393] approximately −90 dBm/Hz at approximately 93.1 kHz;

[0394] approximately −62 dBm/Hz at approximately 209 kHz;

[0395] approximately −36.5 dBm/Hz at approximately 255 kHz;

[0396] approximately −36.5 dBm/Hz at approximately 1104 kHz;

[0397] approximately −46.5 dBm/Hz at approximately 2208 kHz;

[0398] approximately −101.5 dBm/Hz at approximately 3925 kHz;

[0399] approximately −101.5 dBm/Hz at approximately 8500 kHz;

[0400] approximately −103.5 dBm/Hz at approximately 8500 kHz; and

[0401] approximately −103.5 dBm/Hz at approximately 11040 kHz.

[0402] In accordance with another embodiment of the present invention, apower spectral density (PSD) mask for spectral shaping of anasynchronous digital subscriber line (ADSL) overlap spectrum over anintegrated digital services network (ISDN) is provided. The PSD mask maybe represented at least in part by a plurality of break points, theplurality of break points including:

[0403] approximately −90 decibel-milliwatts per hertz (dBm/Hz) atapproximately 0 kilohertz (kHz);

[0404] approximately −90 dBm/Hz at approximately 93.1 kHz;

[0405] approximately −62 dBm/Hz at approximately 209 kHz;

[0406] approximately −56.5 dBm/Hz at approximately 255 kHz;

[0407] approximately −56.5 dBm/Hz at approximately 1104 kHz;

[0408] approximately −46.5 dBm/Hz at approximately 2208 kHz;

[0409] approximately −101.5 dBm/Hz at approximately 3925 kHz;

[0410] approximately −101.5 dBm/Hz at approximately 8500 kHz;

[0411] approximately −103.5 dBm/Hz at approximately 8500 kHz; and

[0412] approximately −103.5 dBm/Hz at approximately 11040 kHz.

[0413] +++++

[0414] In accordance with one embodiment of the present invention, apower spectral density (PSD) mask for spectral shaping of anasynchronous digital subscriber line (ADSL) overlap spectrumtransmission over a plain old telephone system (POTS) is provided. ThePSD mask is represented at least in part by a plurality of break points,the plurality of break points including:

[0415] −97.5±5% decibel-milliwatts per hertz (dBm/Hz) at 0±5% kilohertz(kHz);

[0416] −97.5±5% dBm/Hz at 4±5% kHz;

[0417] −92.5±5% dBm/Hz at 4±5% kHz;

[0418] −36.5±5% dBm/Hz at 25±5% kHz;

[0419] −36.5±5% dBm/Hz at 1104±5% kHz;

[0420] −46.5±5% dBm/Hz at 2208±5% kHz;

[0421] −101.5±5% dBm/Hz at 3925±5% kHz;

[0422] −101.5±5% dBm/Hz at 8500±5% kHz;

[0423] −103.5±5% dBm/Hz at 8500±5% kHz; and

[0424] -103.5±5% dBm/Hz at 11040±5% kHz.

[0425] In accordance with another embodiment of the present invention, apower spectral density (PSD) mask for spectral shaping of anasynchronous digital subscriber line (ADSL) non-overlap spectrum over aplain old telephone system (POTS) is provided. The PSD mask may berepresented at least in part by a plurality of break points, theplurality of break points including:

[0426] −97.5±5% decibel-milliwatts per hertz (dBm/Hz) at 0±5% kilohertz(kHz);

[0427] −97.5±5% dBm/Hz at 4±5% kHz;

[0428] −72.5±5% dBm/Hz at 80±5% kHz;

[0429] −36.5±5% dBm/Hz at 138±5% kHz;

[0430] −36.5±5% dBm/Hz at 1104±5% kHz;

[0431] −46.5±5% dBm/Hz at 2208±5% kHz;

[0432] −101.5±5% dBm/Hz at 3925+5% kHz;

[0433] −101.5±5% dBm/Hz at 8500±5% kHz;

[0434] −103.5±5% dBm/Hz at 8500±5% kHz; and

[0435] −103.5±5% dBm/Hz at 11040±5% kHz.

[0436] In accordance with an additional embodiment of the presentinvention, a power spectral density (PSD) mask for spectral shaping ofan asynchronous digital subscriber line (ADSL) overlap spectrum over aplain old telephone system (POTS) is provided. The PSD mask may berepresented at least in part by a plurality of break points, theplurality of break points including:

[0437] −97.5±5% decibel-milliwatts per hertz (dBm/Hz) at 0±5% kilohertz(kHz);

[0438] −97.5±5% dBm/Hz at 4±5% kHz;

[0439] −92.5±5% dBm/Hz at 4±5% kHz;

[0440] −56.5±5% dBm/Hz at 25±5% kHz;

[0441] −56.5±5% dBm/Hz at 1104±5% kHz;

[0442] −46.5±5% dBm/Hz at 2208±5% kHz;

[0443] −101.5±5% dBm/Hz at 3925±5% kHz;

[0444] −101.5±5% dBm/Hz at 8500±5% kHz;

[0445] −103.5±5% dBm/Hz at 8500±5% kHz; and

[0446] −103.5±5% dBm/Hz at 11040±5% kHz.

[0447] In accordance with another embodiment of the present invention, apower spectral density (PSD) mask for spectral shaping of anasynchronous digital subscriber line (ADSL) non-overlap spectrum over aplain old telephone system (POTS) is provided. The PSD mask may berepresented at least in part by a plurality of break points, theplurality of break points including:

[0448] −97.5±5% decibel-milliwatts per hertz (dBm/Hz) at 0±5% kilohertz(kHz);

[0449] −97.5±5% dBm/Hz at 4±5% kHz;

[0450] −92.5±5% dBm/Hz at 80±5% kHz;

[0451] −56.5±5% dBm/Hz at 138±5% kHz;

[0452] −56.5±5% dBm/Hz at 1104±5% kHz;

[0453] −46.5±5% dBm/Hz at 2208±5% kHz;

[0454] −101.5±5% dBm/Hz at 3925±5% kHz;

[0455] −101.5±5% dBm/Hz at 8500±5% kHz;

[0456] −103.5±5% dBm/Hz at 8500±5% kHz; and

[0457] −103.5±5% dBm/Hz at 11040±5% kHz.

[0458] In accordance with yet another embodiment of the presentinvention, a power spectral density (PSD) mask for spectral shaping ofan asynchronous digital subscriber line (ADSL) overlap spectrum over anintegrated digital services network (ISDN) is provided. The PSD mask maybe represented at least in part by a plurality of break points, theplurality of break points including:

[0459] −90±5% decibel-milliwatts per hertz (dBm/Hz) at 0±5% kilohertz(kHz);

[0460] −90±5% dBm/Hz at 93.1±5% kHz;

[0461] −62±5% dBm/Hz at 209±5% kHz;

[0462] −36.5±5% dBm/Hz at 255±5% kHz;

[0463] −36.5±5% dBm/Hz at 1104±5% kHz;

[0464] −46.5±5% dBm/Hz at 2208±5% kHz;

[0465] −101.5±5% dBm/Hz at 3925±5% kHz;

[0466] −101.5±5% dBm/Hz at 8500±5% kHz;

[0467] −103.5±5% dBm/Hz at 8500±5% kHz; and

[0468] −103.5±5% dBm/Hz at 11040±5% kHz.

[0469] In accordance with another embodiment of the present invention, apower spectral density (PSD) mask for spectral shaping of anasynchronous digital subscriber line (ADSL) overlap spectrum over anintegrated digital services network (ISDN) is provided. The PSD mask maybe represented at least in part by a plurality of break points, theplurality of break points including:

[0470] −90±5% decibel-milliwatts per hertz (dBm/Hz) at 0±5% kilohertz(kHz);

[0471] −90+5% dBm/Hz at 93.1±5% kHz;

[0472] −62±5% dBm/Hz at 209±5% kHz;

[0473] −56.5±5% dBm/Hz at 255±5% kHz;

[0474] −56.5±5% dBm/Hz at 1104±5% kHz;

[0475] −46.5±5% dBm/Hz at 2208±5% kHz;

[0476] −101.5±5% dBm/Hz at 3925±5% kHz;

[0477] −101.5±5% dBm/Hz at 8500±5% kHz;

[0478] −103.5±5% dBm/Hz at 8500±5% kHz; and

[0479] −103.5±5% dBm/Hz at 11040±5% kHz.

[0480] Method and System for Adaptive Shaping:

[0481] To further enhance the performance characteristics of thecommunications system, a method and system for adaptive shaping may beemployed. Such a system has broad applicability well beyond the realm ofG.992, G.994 and other such standards. This system may be thought of asa “smart” DSL or other such system. In one embodiment, the systemutilizes a table or plot for matching optimum or desired systems ormasks with corresponding distances. In one respect, key factors orconsiderations include maximizing downstream data rate, maintainingspectral compliance/compatibility, and minimizing complexity and systemrequirements. In one example, as shown in Table 28, systems are selectedfor short loop lengths to maximize data rate and for long loop lengthsto maximize reach. As shown in this example, a DBMOL system may be usedfor relatively short loop length distances of less than, for example,1.5 km. At distances of between 1.5 km and 2 km, a DBMsOL system or maskis employed. At distances of between 2 km and 3.5 km, an XOL system maybe employed. At distances of between 3.5 km and 5 km a XDD system may beemployed and at distances greater than 5 km an FBMsOL system may beemployed. TABLE 28 Loop Distance System/Mask  <1.5 km DBMOL 1.5-2 kmDBMsOL 2-3.5 km XOL 3.5-5 km XDD   >5 km FBMsOL

[0482] A look-up table or plot may be used as a reference and thesystem. For instance, the central office CO may use the data pointmsg.ra, as is used from ATU-R to ATU-C, to determine the loop length andfrom that to select the appropriate system based on the look up table.This is used to optimize overall system performance by weighingcompeting interests and there differing effects based on systemconditions, such as loop length. At short loop lengths, data rate ismaximized while at longer loop lengths reach is the primary concern.

[0483] Signal Attenuation Considerations:

[0484] Reduced Symbol Rates During the Handshaking Process:

[0485] Messages in G.994.1 are sent with one or more carrier sets. Allcarrier frequencies within a carrier set are simultaneously modulatedwith the same data bits using a Differentially-encoded Binary PhaseShift Keying (DPSK). The signal quality on the carrier frequencies usedfor signaling in the handshake procedures described in G.994.1 oftensuffer heavily from TCM-ISDN noise, particularly in the case of longerloops (typically those having a length greater than 5.5 km). Accordingto the G.994.1 standard, the tolerance of the symbol rates and frequencyfor an HTSU-C are +/−50 parts per million (ppm) and for an HSTU-R are+/−200 ppm during R-TONES-REQ and +/−50 during and after R-TONE1 induplex transmission mode or R-FLAG1 in half-duplex mode. Althoughperturbations are minimized, for example, in the carrier sets in the4.3125 kHz signaling family (carrier sets A43, B43, C43) which usesfrequencies less exposed to this type of cross-talk, TCM-ISDN near endcross-talk (NEXT) noise can severely diminish signal quality. Forexample, in severe cases, six out of eight 4.3125 kHz sub-symbols couldbe affected by NEXT noise, significantly reducing the quality of thesignal.

[0486] Accordingly, at least one embodiment of the present inventionprovides for a process to reduce the effects of noise within loopsduring G.994.1 handshaking procedures by reducing the symbol rate duringthe handshaking process. The symbol rate preferably is reduced byone-half. To illustrate, for carrier sets A43 and C43, the symbol rateof 539.0625 (4312.5/8) symbols per second. However, by reducing the rateto 269.53125 (4312.5/16) symbols per second, at least four sub-symbolsof every symbol will lie outside the NEXT duration and therefore mayonly be affected by far-end crosstalk (FEXT) noise. However, a phasechange detector operating on four sub-symbols typically is robust inFEXT noise environments, thereby limiting the effects of FEXT noise.

[0487] The process by which the reduced symbol rate is implemented canbe implemented in a variety of ways. In one embodiment, a HSTU-C whichopts to select, for example, carrier sets A43 and C43 with reducedsymbol rate (269.53125 symbols per second) can be adapted to respond toR-TONE1 by transmitting Galfs (an octet of value 81 ₁₆, i.e., theones-complement of an HDLC flag) on modulated carriers (C-GALF1) usingthe selected reduced symbol rate. C-GALF1 is an octet of value 81 ₁₆,resulting in a phase transition at the beginning and at the end of eachoctet transmitted. By counting these transitions the HSTU-R can beadapted to determine the symbol rate the HSTU-C has selected in areliable way. This ensures that the HSTU-C keeps control of the mode andin particular if the HSTU-C is in the current standard mode then theHSTU-R will not transition to a reduced rate mode thereby ensuringbackward compatibility. The HSTU-C then would maintain this reducedsymbol rate throughout the subsequent handshake procedure.

[0488] Similarly, the corresponding HSTU-R capable of operation inreduced symbol rate mode could be adapted to respond to C-GALF1 bytransmitting, for example, Flags on modulated carriers (R-FLAG1) usingthe reduced symbol rate detected in C-GALF1. The HSTU-R typically wouldmaintain this reduced symbol rate throughout the subsequent handshakeprocedure. If an HSTU-R is not capable of operation in reduced symbolrate mode, the HSTU-R could switch to state R-SILENT0.

[0489] It may be desirable to maintain a backward compatibility withHSTU-Rs that are not capable of the desired reduced symbol rate mode.Accordingly, the HSTU-C capable of reduced symbol rate mode can beadapted to toggle between regular rate and reduced rate after eachfailed handshake attempt to ensure backward compatibility. Furthermore,should multiple reduced symbol rates be available for the handshakeprocess, the HSTU-C could be adapted to cycle through all availablesymbol rates after each failed handshake attempt until a symbol ratecompatible with the corresponding HSTU-R is found. In at least oneembodiment, the reduced symbol rate mode during handshaking can beachieved without prior synchronization with a signal sent by an ATU-C.

[0490] The reduced symbol rate handshake process describe above may beimplemented for carrier sets A43 and C43 using the following exemplarychanges to the ITU G.994.1 standard:

[0491] The insertion of the following sub-section 6.1.1.1 below section6.1.1 in G.994.1—

[0492] 6.1.1.1 Optional Reduction of Symbol Rate

[0493] For carrier sets A43 and C43, a symbol rate of4312.5/16≡269.53125 symbols per second may be used.

[0494] The insertion of the following section 11.1.3 below section11.1.2 in G.994.1—

[0495] 11.1.3 Duplex Start-Up Procedure with Reduced Symbol Rate

[0496] A HSTU-C which chooses to select carrier sets A43 and C43 withreduced symbol rate (269.53125 symbols per second) may respond toR-TONE1 by transmitting Galfs on modulated carriers (C-GALF1) using thereduced symbol rate. C-GALF1 is an octet of value 81 ₁₆, i.e. a phasetransition at the beginning and at the end of each octet will betransmitted. By counting these transitions, the HSTU-R can determine thesymbol rate the HSTU-C has chosen in a reliable way. This ensures theHSTU-C keeps control of the mode and, in particular, if the HSTU-C is inthe current standard mode then the HSTU-R will not transition to areduced rate mode thereby ensuring backward compatibility. It maymaintain this symbol rate throughout the subsequent handshake procedure.

[0497] A HSTU-R capable of operation in reduced symbol rate mode mayrespond to C-GALF1 by transmitting Flags on modulated carriers (R-FLAG1)using the symbol rate detected in C-GALF1. It may maintain this symbolrate throughout the subsequent handshake procedure. A HSTU-R which isnot capable of operation in reduced symbol rate mode may switch to stateR-SILENT0. A HSTU-C capable of reduced symbol rate mode may togglebetween regular rate and reduced rate after each failed handshakeattempt to ensure backward compatibility.

[0498] The reduced symbol rate handshake procedure detailed above oftenovercomes the shortcomings of a receiver during handshaking under strongTCM-ISDN conditions. Therefore receiver-focused reduced symbol ratetechnique can be applied to complete a robust handshake. In this case,an HSTU-R can be adapted to derive a 400 Hz local reference clock bymonitoring the TCM-ISDN noise level when the difference between the FEXTand NEXT noise levels is, for example, at least 3 dB. FIG. 16illustrates exemplary results obtained using averaging over 32 TCM-ISDNperiods (80 ms).

[0499] The HTSU-R then can discard the stronger NEXT-phase and retainonly the FEXT-phase throughout the handshake procedure. In the case ofstationary white noise (difference between NEXT and FEXT noise levelsof, for example, less than 3 dB), above “noise gating” may not beapplied and the HTSU-R can use all sixteen 4.3125 kHz sub-symbols withinone handshake symbol. The advantage of this procedure is the performanceimprovement with respect to the handshake currently defined by theG.994.1 standard as well as with respect to the case where only FEXTsub-symbols are processed.

[0500]FIG. 17 illustrates a simulated performance of an exemplary HTSU-Rreceiver utilizing a handshake symbol reduction rate of one-half forcarrier set C43. In the illustrated simulation, the signal-to-noise(SNR) on tone 14 (2^(nd) down stream tone in carrier set C43) in thepresence of 24 TCM-ISDN disturbers is assumed to be approximately −16 dBduring NEXTR phases and greater than 30 dB during FEXT_(R) periods at adistance of 7 km. The simulated HSTU-R receiver, as illustrated, workssufficiently at an SNR_(FEXT) of 6 dB, an SNR_(NEXT) of −16 dB. Alsoincluded in the simulation is the case where the local 400 Hz TCM-ISDNclock at the HSTU-R has a phase offset with respect to the TCM-ISDNnoise (i.e. the noise gate will let sub-symbols partially affected byNEXT noise pass and will block others that lie entirely with in the FEXTduration). FIG. 17 illustrates that the reduced symbol rate in thesimulated HTSU-R receiver works reliably under SNR conditions and aTCM-ISDN phase offset of ⅛ of a 4.3125 kHz sub-symbol (29 μs). Understationary white noise conditions, the receiver works well at asignal-to-noise ratio (SNR) of 3 dB.

[0501] Modification of TTR and Pilot Tones for Extended ReachApplications:

[0502] G.992.1 Annex C compliant extended reach systems often utilizeoverlap mode to increase the downstream bandwidth in data mode. At verylong distances (typically greater than 6 km), certain tones, such as thePILOT 64 and TTR 48, exhibit considerable drop in their SNR, resultingin faulty operation and/or substandard performance of the system. Toillustrate, FIGS. 18 and 19 display exemplary plots of, respectively,PILOT 64 and TTR 48 SNR versus distance in the presence of −140 dBm/Hzwhite noise when using 0.4 mm paper insulated cable. FIGS. 20 and 21display, respectively, exemplary plots of PILOT 64 and TTR 48 SNR versusdistance in the presence of 24 TCM-ISDN disturbers.

[0503] The illustrated results of laboratory testing has shown that inthe presence of −140 dBm/Hz white noise, TTR & Pilot detectionalgorithms using tones PILOT 64 and TTR 48 generally only work up toabout 6.2 km when 0.4 mm paper insulated cable is used. To extend thepossible range during TTR and Pilot detection, the present inventionprovides for a process for using alternate tones, such as PILOT 34 andTTR 24, in extended reach systems due to the less significant drop inSNR exhibited by these tones over long distances. FIGS. 22 and 23display exemplary plots of, respectively, PILOT 32 and TTR 24 SNR versusdistance in the presence of −140 dBm/Hz white noise using 0.4 mm paperinsulated cable. FIGS. 24 and 25 display exemplary plots of,respectively, PILOT 32 and TTR 24 SNR versus distance in the presence of24 TCM-ISDN disturbers.

[0504] As FIGS. 22-25 illustrate, the PILOT 32 tone and the TTR 24 toneexhibit significantly better SNR at extended distances compared to thePILOT 32 and TTR 24 tones, respectively. For example, the PILOT tone 64SNR is about 0 dB at approximately 6.2 km in the presence of white noisewhereas the PILOT tone 32 SNR is about +15 dB at about 7.0 km. Likewise,the TTR 48 SNR is equal to about +13 dB at approximately 6.2 km in thepresence of the white noise whereas the TTR 24 SNR is equal to about +25dB at approximately 7.0 km. Accordingly, the PILOT 32 and TTR 24 tonescan be expected to reach about 7 km, whereas the PILOT 64 and TTR 48 canbe expected to reach only about 6.2 km.

[0505] Pilot 64 and TTR 48 Limitations in FDM Mode:

[0506] FDM-compliant systems often are limited to less than 4 km innoise-laden environments, such as Japan. Accordingly, Pilot 64 and TTR48 detection techniques may fail in the FDM mode in such instances.Reasons that may lead to TTR & PILOT failures include the presence of 24TCM-ISDN; several bridge taps zeroing the spectrum in the vicinity oftones 48 & 64; the loop plant of the system being close to the 4 kmlimit; and the like. Accordingly, a testing scenario that wouldsufficiently assess PILOT 64 and TTR 48 limitations in the FCM modetypically would include features such as: a 4 km long loop; 0.4 mm paperinsulated cable; 24 TCM-ISDN cross talks; an increasing number of ˜190 mlong bridge taps (190 m long bridge tap zeroes the loop frequencyresponse in the vicinity of tones 64 & 48); and the like.

[0507]FIG. 26 illustrates the loop attenuation vs. frequency accordingto the number of bridge taps in such a testing scenario. This testingscenario typically represents a negligible fraction of the factors thatreduce signal quality in actual field implementations. Straight 0.4 mmpaper loops in Japan and combined with six bridge taps zeroing exactlythe vicinity of tones 64 and 48 decreases the likelihood of such a caseeven more. Therefore, although it is always possible to define ascenario that leads to TTR 48 and PILOT 64 failures in the FDM mode, thehigh margin exhibited even in this optimistic loop scenario isindicative of implementation limitations rather than physical layerintrinsic bounds.

[0508] Tables 29 and 30 illustrate exemplary TTR 48 and PILOT 64 SNRboth in the white noise scenario and in the presence of 24 TCM-ISDNversus the number of bridge taps. These tables illustrate that TTR 48and PILOT 64 exhibit more than 10 dB margin with respect to the minimumrequired SNR. TABLE 29 TTR 48 Bridge Taps 24 TCM-ISDN BT number AWGNFEXT NEXT 0 43.85 32.85 −14.95 1 36.66 31.59 −22.14 2 32.62 29.90 −26.173 29.86 28.21 −28.93 4 27.76 26.67 −31.03 5 26.07 25.30 −32.72 6 24.6524.09 −34.14

[0509] TABLE 30 Tone Pilot 64 Bridge Taps TCM-ISDN number AWGN FEXT NEXT0 36.28 34.31 −16.39 1 30.37 29.78 −22.30 2 26.74 26.47 −25.93 3 24.1624.01 −28.51 4 22.17 22.07 −30.50 5 20.55 20.48 −32.13 6 19.18 19.13−33.50

[0510] To allow the optional use of the PILOT 32 tone and the TTR 24tone as additional or alternate tones for extended reach respectivelyfor pilot tone and TTR signal the following exemplary amendments andadditions to the G.994.1 and G.992.1 standards can be implemented.

[0511] Changes in G.994.1:

[0512] In G.994.1, a code point can be added to signal to HTU-R/HTU-C toprovide the capability of transmitting/receiving Pilot Tone on tone 32and TTR tone on A24. The following Tables 31 and 31 illustrate theaddition of the code point. TABLE 31 Standard information field -G.992.1 Annex C SPar(2) coding Bits 8 7 6 5 4 3 2 1 G.992.1 Annex CSPar(2)s x x x x x x x 1 Sub-channel information x x x x x x 1 xSpectrum frequency upstream x x x x x 1 x x Spectrum frequencydownstream x x x x 1 x x x C-PILOT x x x 1 x x x x Reserved forallocation by the ITU-T x x 1 x x x x x Reserved for allocation by theITU-T x x 0 0 0 0 0 0 No parameters in this octet

[0513] TABLE 32 Standard information field - G.992.1 Annex C C-PILOTNPar(3) coding Bits G.992.1 Annex C C-PILOT 8 7 6 5 4 3 2 1 NPar(3)s x xx x x X x 1 n_(C-PILOT1) = 32 x x x x x X 1 x A₂₄ x x x x x 1 x xReserved for allocation by the ITU-T x x x x 1 X x x Reserved forallocation by the ITU-T x x x 1 x X x x Reserved for allocation by theITU-T x x 1 x x X x x Reserved for allocation by the ITU-T x x 0 0 0 0 00 No parameters in this octet

[0514] Changes in G.992.1:

[0515] The following bit definitions can be supplemented as follows:

[0516] In Annex C.7.2—Handshake—ATU-C (supplements § 10.2):

[0517] C.7.2.1CL messages (supplements § 10.2.1) can be supplemented asillustrated in Table 33. TABLE 33 ATU-C CL message NPar(3) bitdefinitions for Annex C NPar(3) bit Definition n_(C-PILOT1) = 32 If setto ZERO, this bit may indicate that the ATU-C will transmit the defaultpilot tone 64 in training and data mode. If set to ONE, this bit mayindicate that the ATU-C will transmit the optional pilot tone 32 insteadof pilot tone 64. Note: to ensure backward compatibility the ATU-C willonly set this bits to ONE if the corresponding Npar(3) bit in CLR is setto ONE. A24 If set to ZERO, this bit may indicate that the ATU-C willtransmit the default TTR tone 48 in C-Pilot1A. If set to ONE, this bitmay indicate that the ATU-C will transmit the optional TTR tone 24instead of TTR tone 48 in C-Pilot1A. Note: to ensure backwardcompatibility the ATU_C will only set this bits to ONE if thecorresponding Npar(3) bit in CLR is set to ONE.

[0518] In Annex C.7.3—Handshake—ATU-R (supplements § 10.3):

[0519] C.7.3.1CLR messages (supplements § 10.3.1) can be supplemented asillustrated by Table 34. TABLE 34 ATU-R CLR message NPar(3) bitdefinitions for Annex C NPar(3) bit Definition n_(C-PILOT1) = 32 If setto ZERO, this bit may indicate that the ATU-R is not capable ofreceiving pilot tone 32, besides pilot tone 64. If set to ONE, this bitmay indicate that the ATU-R is capable of receiving pilot tone 32,besides pilot tone 64. Note: to ensure backward compatibility the ATU_Rmay only assume that ATU-C will transmit on pilot tone 32, only if thecorresponding Npar(3) bit in CL is set to ONE. A24 If set to ZERO, thisbit may indicate that the ATU-R is not capable of receiving TTR toneA24, besides TTR tone A48 in C-pilot1A. If set to ONE, this bit mayindicate that the ATU-R is capable of receiving TTR tone A24, besidesTTR tone A48. Note: to ensure backward compatibility the ATU_R mayassume that ATU-C will transmit on TTR Tone A24, if the correspondingNpar(3) bit in CL is set to ONE.

[0520] The present invention provides for the tones PILOT 32 and TTR 24to be used as optional tones in the Annex C overlap mode for extendedreach beyond, for example, 6.2 km as under this reach the currentdefinition of these tones are sufficient for a robust startup. Based onthese practical reaches and the SNR of tones 64 & 48 dependency versusdistance as described in the above figures, practical SNR toneslimitations both in the white noise case scenario and in the presence of24 TCM-ISDN interferers can be determined.

[0521] To summarize, one embodiment of the present invention providedfor a method in an asynchronous digital subscriber line (ADSL) systemcomprising a central office ADSL Terminating Unit (ATU-C) inbi-directional overlap spectrum discrete multitone (DMT) communicationwith a remote ADSL Terminating Unit (ATU-R). The method comprises thestep of transmitting a first handshake tone at either a first DMT toneor a second DMT tone based at least in part on a distance between theATU-C and ATU-R. In one embodiment, the first handshake tone istransmitted at the first DMT tone when the distance between the ATU-Cand ATU-R is less than 6.2 kilometers and the first handshake tone istransmitted at the second DMT tone when the distance between the ATU-Cand ATU-R is greater than or equal to 6.2 kilometers. In one embodiment,the first handshake tone is a Pilot tone, the first DMT tone is tone 64and the second DMT tone is tone 32. In another embodiment, the firsthandshake tone is a TCM-ISDN Timing Reference (TTR) tone, the first DMTtone is tone 48 and the second DMT tone is tone 24. The ATU-C and theATU-R preferably are in bidirectional communication via a TCM-ISDNnetwork.

[0522] The method further may comprise the step of transmitting a secondhandshake tone at either a third DMT tone or a fourth DMT tone based atleast in part on the distance between the ATU-C and ATU-R. The secondhandshake tone may be transmitted at the third DMT tone when thedistance between the ATU-C and ATU-R may be less than 6.2 kilometers andthe second handshake tone is transmitted at the fourth DMT tone when thedistance between the ATU-C and ATU-R is greater than or equal to 6.2kilometers. In one embodiment, the first handshake tone is a Pilot toneand the second handshake tone is a TCM-ISDN Timing Reference (TTR) tone,the first DMT tone is tone 64, the second DMT tone is tone 32, the thirdDMT tone is tone 48 and the fourth DMT tone is tone 24.

[0523] To further summarize, an asynchronous digital subscriber line(ADSL) system is provided in accordance with an additional embodiment ofthe present invention. The ADSL system comprises a central office ADSLTerminating Unit (ATU-C) and a remote ADSL Terminating Unit (ATU-R) inbi-directional overlap spectrum discrete multitone (DMT) communicationwith the ATU-C. The ATU-C is adapted to transmit a first handshake toneat either a first DMT tone or a second DMT tone based at least in parton a distance between the ATU-C and ATU-R and the ATU-R is adapted toreceive the first handshake tone at either the first DMT tone or thesecond DMT tone. In one embodiment, the first handshake tone istransmitted at the first DMT tone when the distance between the ATU-Cand ATU-R is less than 6.2 kilometers and the first handshake tone istransmitted at the second DMT tone when the distance between the ATU-Cand ATU-R is greater than or equal to 6.2 kilometers. In one embodiment,the first handshake tone is a Pilot tone, the first DMT tone is tone 64and the second DMT tone is tone 32. In another embodiment, the firsthandshake tone is a TCM-ISDN Timing Reference (TTR) tone, the first DMTtone is tone 48 and the second DMT tone is tone 24. The ATU-C and theATU-R preferably are in bidirectional communication via a TCM-ISDNnetwork.

[0524] The ATU-C further may be adapted to transmit a second handshaketone at either a third DMT tone or a fourth DMT tone based at least inpart on the distance between the ATU-C and ATU-R. The second handshaketone may be transmitted at the third DMT tone when the distance betweenthe ATU-C and ATU-R may be less than 6.2 kilometers and the secondhandshake tone is transmitted at the fourth DMT tone when the distancebetween the ATU-C and ATU-R is greater than or equal to 6.2 kilometers.In one embodiment, the first handshake tone is a Pilot tone and thesecond handshake tone is a TCM-ISDN Timing Reference (TTR) tone, thefirst DMT tone is tone 64, the second DMT tone is tone 32, the third DMTtone is tone 48 and the fourth DMT tone is tone 24.

[0525] Further, the ATU-C may be adapted to transmit the first handshaketone at the first DMT tone when the distance between the ATU-C and ATU-Ris less than 6.2 kilometers and transmit the first handshake tone at thesecond DMT tone when the distance between the ATU-C and ATU-R is greaterthan or equal to 6.2 kilometers.

[0526] Detection and Determination of Symbol Rate of C-GALF1 in G.994.1Handshake Procedure:

[0527] In accordance with yet another embodiment of the presentinvention, the symbol rate of the 4.3125 kHz signaling family describedin section 6.1 of ITU recommendation G.994.1 (Handshake procedures fordigital subscriber line (DSL) transceivers) is optionally lowered from4312.5/8-539.0625 to 4312.5/16-269.53125 symbols per second. The HSTU-C(CO) selects one of the two rates and transmits at this rate beginningwith C-GALF1. The HSTU-R then derives the selected rate by monitoringC-GALF1 and responds by sending R-FLAG1 at this rate. The purpose oflowering the symbol rate is to achieve greater robustness of handshakeprocedures especially in the presence of TCM-ISDN noise. In accordancewith this embodiment, a new type of detector at the HSTU-R is describedherein to detect reliably C-GALF1, based on transition counts. This newdetector will then be essential in determining the symbol rate theHSTU-C has chosen for transmission of C-GALF1.

[0528] Detection of a C-GALF1 Based on a Transition Counts:

[0529] The modulation employed in the G.994.1 Recommendation isDifferentially encoded binary Phase Shift Keying (DPSK), where atransmit bit of value 1 is transmitted as 180° phase shift, and a valueof 0 is transmitted as 0° phase shift, applied simultaneously to allcarriers of the carrier set.

[0530] For demodulation in the receiver, the time-domain signal isdivided into sub-symbols of 231.88 μs (1/43125 Hz) duration, each ofwhich is then the input of an FFT (Fast Fourier Transform). The FFT rateis thus 8 or 16 times the handshake symbol rate. Eight consecutive FFToutput bins at carrier frequencies C(k) are then summed and multipliedwith the sum of the eight previous sub-symbols: $\begin{matrix}{{d(n)} = {\sum\limits_{k = n}^{n - 7}{{C(k)} \cdot {\sum\limits_{k = {n - 8}}^{n - 15}{C(k)}}}}} & {{EQ}.\quad 18} \\{where} & \quad \\{{A \cdot B} = {{{Re}{\left\{ A \right\} \cdot {Re}}\left\{ B \right\}} + {{Im}{\left\{ A \right\} \cdot {Im}}{\left\{ B \right\}.}}}} & {{EQ}.\quad 19}\end{matrix}$

[0531] The sign of d(n) will be negative at each phase change of thecarrier signal. C-GALF is an octet of value 81 ₁₆ and contains two phasechanges. Since the symbol alignment is unknown at this point, thereceiver may simply count the number of sub-symbols with negative d(n)within a given time window in order to determine the presence of C-GALFand to discriminate it from noise or any other received signal.Alternatively, in a “Dual-Rate” C-GALF1, there can be either 5 or 3phase changes within 20 sub-symbols following the first phasetransition, depending on the symbol rate from the HSTU-C. The receivermay switch into the “C-GALF1 detected” state if it has detected aminimum of 3 phase changes within 20 sub-symbols.

[0532] Detection of a “Dual-Rate” C-GALF1 & Determination of the SymbolRate:

[0533] In detection of a “Dual-Rate” C-GALF1, the HSTU-R detector of thepresent invention counts the negative pulses of d(n) over a determinedtime span in order to determine the symbol rate. Section 11.1.1 of theG.994.1 Recommendation specifies that the HSTU-R must respond within 500ms (τ₁<500 ms) after the beginning of C-GALF1. After having detected thepresence of C-GALF1 as explained above in section 1, the HSTU-R countsthe transitions which occur within e.g., 2048 sub-symbols (≈475 ms) anddecides upon the counter value which symbol rate the HSTU-C hasselected. The counter will have a value of 32 if the symbol rateselected is 269.53125, and 64 if the symbol rate is 539.0625. Any periodshorter than 475 ms may also be used.

[0534] To summarize:

[0535] In an asynchronous digital subscriber line (ADSL) systemcomprising a central office High Speed ADSL Terminating Unit (HSTU-C) inbi-directional discrete multitone (DMT) communication with a remote HighSpeed ADSL Terminating Unit (HSTU-R), a method for improving handshakedetection is provided in accordance with an additional embodiment. Themethod comprises transmitting handshake signaling from the HSTU-C to theHSTU-R via a first subset of carrier sets at a first symbol rate andtransmitting handshake signaling from the HSTU-C to the HSTU-R via asecond subset of carrier sets at a second symbol rate, the second symbolrate being less than the first symbol rate. The first symbol ratepreferably is 539.0625 symbols per second and the second symbol ratepreferably is 269.53125 symbols per second. In one embodiment, thehandshake signaling is transmitted via the second subset of carrier setsat the second symbol rate after a handshake attempt between the HSTU-Cand the HSTU-R performed at the first symbol rate for both the first andsecond carrier sets has failed. The second subset of carrier setsincludes carrier sets with noise greater than noise present in the firstsubset of carrier sets, where the noise includes near end cross talk.The second subset of carrier sets preferably includes carrier set C43and the second subset of carrier sets preferably includes carrier setA43. The HSTU-C and HSTU-R preferably are in bidirectional communicationvia a TCM-ISDN network.

[0536] The method further may comprise the step of detecting, at theHSTU-R, a number of phase changes in a given time window of thehandshake signaling transmitted by the HSTU-C via the second subset ofcarrier sets to identify the second symbol rate. The method also maycomprise the step of receiving, at the HSTU-C, at least one handshakesymbol from the HSTU-R at the identified handshake symbol transmissionrate. The step of detecting the number of phase changes in a given timewindow of the handshake signaling includes separating the handshakesignaling transmitted by the HSTU-C into a first set of sub-symbols anda second set of sub-symbols for a given time window, the second set ofsub-symbols following the first set of sub-symbols, performing a fastfourier transform on each of the first set of sub-symbols, performing afast fourier transform on each of the second set of sub-symbols, summinga result of the fast fourier transforms performed on the first set ofsub-symbols, summing a result of the fast fourier transforms performedon the second set of sub-symbols, and multiplying the summed result fromthe first set of sub-symbols with the summed result of the second set ofsub-symbols to determine the number of phase changes in the handshakesignaling within the time window. The number of phase changes detectedwithin the time window may be proportional to the identified secondsymbol rate or the second symbol rate may be identified by the HSTU-Rwhen the number of phase changes is at or above a minimum number ofphase changes associated with second symbol rate.

[0537] In an asynchronous digital subscriber line (ADSL) systemcomprising a central office High Speed ADSL Terminating Unit (HSTU-C) inbi-directional discrete multitone (DMT) communication with a remote HighSpeed ADSL Terminating Unit (HSTU-R), a method for improving handshakedetection robustness is provided. The method comprises transmittinghandshake signaling via a first subset of carrier sets of a DMTtransmission bandwidth between the HSTU-C and HSTU-R at a first symbolrate, determining a presence of near end cross talk (NEXT) in a secondsubset of carrier sets of the DMT transmission bandwidth, andtransmitting the at least one handshake symbol via the second subset ofcarrier sets at a second symbol rate so that at least one sub-symbol ofthe at least one handshake symbol transmitted over the second subset ofcarrier sets is substantially unaffected by near end cross talk. Thefirst symbol rate preferably is 539.0625 symbols per second and thesecond symbol rate preferably is 269.53125 symbols per second. Thesecond subset of carrier sets preferably includes carrier sets C43and/or A43.

[0538] In accordance with an additional embodiment of the presentinvention, an asynchronous digital subscriber line (ADSL) system isprovided. The ADSL system comprises a central office High Speed ADSLTerminating Unit (HSTU-C) and a remote High Speed ADSL Terminating Unit(HSTU-R) in bi-directional discrete multitone (DMT) communication withthe HSTU-C. The HSTU-C is adapted to transmit handshake signaling to theHSTU-R via a first subset of carrier sets at a first symbol rate andtransmit handshake signaling to the HSTU-R via a second subset ofcarrier sets at a second symbol rate, the second rate being less thanthe first rate. The first symbol rate preferably is 539.0625 symbols persecond and the second symbol rate preferably is 269.53125 symbols persecond. The HSTU-C may be further adapted to transmit the handshakesignaling via the second subset of carrier sets at the second rate aftera handshake attempt between the HSTU-C and the HSTU-R performed at thefirst rate for both the first and second carrier sets has failed. Thesecond subset of carrier sets preferably includes carrier set C43 and/orA43.

[0539] In an asynchronous digital subscriber line (ADSL) systemcomprising a central office High Speed ADSL Terminating Unit (HSTU-C) inbi-directional discrete multitone (DMT) communication with a remote HighSpeed ADSL Terminating Unit (HSTU-R), a method for improving handshakedetection is provided in accordance with yet another embodiment of thepresent invention. The method comprises detecting, at the HSTU-R, anumber of phase changes in a given time window of a handshake signalingtransmitted by the HSTU-C to identify a symbol rate of the handshakesignaling. The method further may comprise transmitting anacknowledgement symbol from the HSTU-R to the HSTU-C at the identifiedsymbol rate. The method additionally may comprise receiving, at theHSTU-C, at least one handshake symbol at the HSTU-R at the identifiedsymbol rate.

[0540] The step of detecting the number of phase changes in a given timewindow of the handshake signaling transmitted by the HSTU-C to identifya symbol rate of the handshake signaling preferably includes separatingthe handshake signaling transmitted by the HSTU-C into a first set ofsub-symbols and a second set of sub-symbols for a given time window, thesecond set of sub-symbols following the first set of sub-symbols,performing a fast fourier transform on each of the first set ofsub-symbols, performing a fast fourier transform on each of the secondset of sub-symbols, summing a result of the fast fourier transformsperformed on the first set of sub-symbols, summing a result of the fastfourier transforms performed on the second set of sub-symbols, andmultiplying the summed result from the first set of sub-symbols with thesummed result of the second set of sub-symbols to determine the numberof phase changes of the handshake signaling within the time window. Thenumber of phase changes detected within the time window may beproportional to the identified symbol rate or the identified symbol ratemay be identified by the HSTU-R when the number of phase changes is ator above a minimum number of phase changes associated with theidentified symbol rate.

[0541] While the foregoing description includes many details andspecificities, it is to be understood that these have been included forpurposes of explanation only, and are not to be interpreted aslimitations of the present invention. Many modifications to theembodiments described above can be made without departing from thespirit and scope of the present invention.

What is claimed is:
 1. In an asynchronous digital subscriber line (ADSL)system comprising a central office High Speed ADSL Terminating Unit(HSTU-C) in bi-directional discrete multitone (DMT) communication with aremote High Speed ADSL Terminating Unit (HSTU-R), a method for improvinghandshake detection comprising: transmitting handshake signaling fromthe HSTU-C to the HSTU-R via a first subset of carrier sets at a firstsymbol rate; and transmitting handshake signaling from the HSTU-C to theHSTU-R via a second subset of carrier sets at a second symbol rate, thesecond symbol rate being less than the first symbol rate.
 2. The methodas in claim 1, wherein the first symbol rate is 539.0625 symbols persecond.
 3. The method as in claim 2, wherein the second symbol rate is269.53125 symbols per second.
 4. The method as in claim 1, wherein thesecond symbol rate is 269.53125 symbols per second.
 5. The method as inclaim 1, wherein the handshake signaling is transmitted via the secondsubset of carrier sets at the second symbol rate after a handshakeattempt between the HSTU-C and the HSTU-R performed at the first symbolrate for both the first and second carrier sets has failed.
 6. Themethod as in claim 1, wherein the second subset of carrier sets includescarrier sets with noise greater than noise present in the first subsetof carrier sets.
 7. The method as in claim 1, wherein the noise includesnear end cross talk.
 8. The method as in claim 1, wherein the secondsubset of carrier sets includes carrier set C43.
 9. The method as inclaim 1, wherein the second subset of carrier sets includes carrier setA43.
 10. The method as in claim 1, wherein the HSTU-C and HSTU-R are inbidirectional communication via a TCM-ISDN network.
 11. The method as inclaim 1, further comprising the step of: detecting, at the HSTU-R, anumber of phase changes in a given time window of the handshakesignaling transmitted by the HSTU-C via the second subset of carriersets to identify the second symbol rate.
 12. The method of claim 11,further comprising the step of: receiving, at the HSTU-C, at least onehandshake symbol from the HSTU-R at the identified handshake symboltransmission rate.
 13. The method as in claim 11, wherein the step ofdetecting the number of phase changes in a given time window of thehandshake signaling includes: separating the handshake signalingtransmitted by the HSTU-C into a first set of sub-symbols and a secondset of sub-symbols for a given time window, the second set ofsub-symbols following the first set of sub-symbols; performing a fastfourier transform on each of the first set of sub-symbols; performing afast fourier transform on each of the second set of sub-symbols; summinga result of the fast fourier transforms performed on the first set ofsub-symbols; summing a result of the fast fourier transforms performedon the second set of sub-symbols; multiplying the summed result from thefirst set of sub-symbols with the summed result of the second set ofsub-symbols to determine the number of phase changes in the handshakesignaling within the time window.
 14. The method of claim 13, whereinthe number of phase changes detected within the time window isproportional to the identified second symbol rate.
 15. The method ofclaim 13, wherein the second symbol rate is identified by the HSTU-Rwhen the number of phase changes is at or above a minimum number ofphase changes associated with second symbol rate.
 16. In an asynchronousdigital subscriber line (ADSL) system comprising a central office HighSpeed ADSL Terminating Unit (HSTU-C) in bidirectional discrete multitone(DMT) communication with a remote High Speed ADSL Terminating Unit(HSTU-R), a method for improving handshake detection robustnesscomprising: transmitting handshake signaling via a first subset ofcarrier sets of a DMT transmission bandwidth between the HSTU-C andHSTU-R at a first symbol rate; determining a presence of near end crosstalk (NEXT) in a second subset of carrier sets of the DMT transmissionbandwidth; and transmitting the at least one handshake symbol via thesecond subset of carrier sets at a second symbol rate so that at leastone sub-symbol of the at least one handshake symbol transmitted over thesecond subset of carrier sets is substantially unaffected by near endcross talk.
 17. The method as in claim 16, wherein the first symbol rateis 539.0625 symbols per second.
 18. The method as in claim 17, whereinthe second symbol rate is 269.53125 symbols per second.
 19. The methodas in claim 16, wherein the second symbol rate is 269.53125 symbols persecond.
 20. The method as in claim 16, wherein the second subset ofcarrier sets includes carrier set C43.
 21. The method as in claim 16,wherein the second subset of carrier sets includes carrier set A43. 22.An asynchronous digital subscriber line (ADSL) system comprising: acentral office High Speed ADSL Terminating Unit (HSTU-C); and a remoteHigh Speed ADSL Terminating Unit (HSTU-R) in bi-directional discretemultitone (DMT) communication with the HSTU-C; wherein the HSTU-C isadapted to: transmit handshake signaling to the HSTU-R via a firstsubset of carrier sets at a first symbol rate; and transmit handshakesignaling to the HSTU-R via a second subset of carrier sets at a secondsymbol rate, the second rate being less than the first rate.
 23. TheADSL system as in claim 22, wherein the first symbol rate is 539.0625symbols per second.
 24. The ADSL system as in claim 23, wherein thesecond symbol rate is 269.53125 symbols per second.
 25. The ADSL systemas in claim 22, wherein the second symbol rate is, 269.53125 symbols persecond.
 26. The ADSL system as in claim 22, wherein the HSTU-C isfurther adapted to transmit the handshake signaling via the secondsubset of carrier sets at the second rate after a handshake attemptbetween the HSTU-C and the HSTU-R performed at the first rate for boththe first and second carrier sets has failed.
 27. The ADSL system as inclaim 22, wherein the second subset of carrier sets includes carriersets with noise interference greater than noise interference present inthe first subset of carrier sets.
 28. The ADSL system as in claim 22,wherein the noise interference includes near end cross talk.
 29. TheADSL system as in claim 22, wherein the second subset of carrier setsincludes carrier set C43.
 30. The ADSL system as in claim 22, whereinthe second subset of carrier sets includes carrier set A43.
 31. The ADSLsystem as in claim 22, wherein the HSTU-C and HSTU-R are inbidirectional communication via a TCM-ISDN network.
 32. In anasynchronous digital subscriber line (ADSL) system comprising a centraloffice High Speed ADSL Terminating Unit (HSTU-C) in bidirectionaldiscrete multitone (DMT) communication with a remote High Speed ADSLTerminating Unit (HSTU-R), a method for improving handshake detectioncomprising: detecting, at the HSTU-R, a number of phase changes in agiven time window of a handshake signaling transmitted by the HSTU-C toidentify a symbol rate of the handshake signaling.
 33. The method ofclaim 32, further comprising the step of: transmitting anacknowledgement symbol from the HSTU-R to the HSTU-C at the identifiedsymbol rate.
 34. The method of claim 32, further comprising the step of:receiving, at the HSTU-C, at least one handshake symbol at the HSTU-R atthe identified symbol rate.
 35. The method as in claim 32, wherein thestep of detecting the number of phase changes in a given time window ofthe handshake signaling transmitted by the HSTU-C to identify a symbolrate of the handshake signaling includes: separating the handshakesignaling transmitted by the HSTU-C into a first set of sub-symbols anda second set of sub-symbols for a given time window, the second set ofsub-symbols following the first set of sub-symbols; performing a fastfourier transform on each of the first set of sub-symbols; performing afast fourier transform on each of the second set of sub-symbols; summinga result of the fast fourier transforms performed on the first set ofsub-symbols; summing a result of the fast fourier transforms performedon the second set of sub-symbols; multiplying the summed result from thefirst set of sub-symbols with the summed result of the second set ofsub-symbols to determine the number of phase changes of the handshakesignaling within the time window.
 36. The method of claim 32, whereinthe number of phase changes detected within the time window isproportional to the identified symbol rate.
 37. The method of claim 32,wherein the identified symbol rate is identified by the HSTU-R when thenumber of phase changes is at or above a minimum number of phase changesassociated with the identified symbol rate.